diff --git a/src/core/mentions/__tests__/resolveImageMentions.spec.ts b/src/core/mentions/__tests__/resolveImageMentions.spec.ts
index 9169f40ef7..c0c57d3f63 100644
--- a/src/core/mentions/__tests__/resolveImageMentions.spec.ts
+++ b/src/core/mentions/__tests__/resolveImageMentions.spec.ts
@@ -1,6 +1,7 @@
 import * as path from "path"
 
 import { resolveImageMentions } from "../resolveImageMentions"
+import { formatResponse } from "../../prompts/responses"
 
 vi.mock("../../tools/helpers/imageHelpers", () => ({
 	isSupportedImageFormat: vi.fn((ext: string) =>
@@ -11,9 +12,12 @@ vi.mock("../../tools/helpers/imageHelpers", () => ({
 	readImageAsDataUrlWithBuffer: vi.fn(),
 	validateImageForProcessing: vi.fn(),
 	ImageMemoryTracker: vi.fn().mockImplementation(function () {
+		let totalMemoryUsed = 0
 		return {
-			getTotalMemoryUsed: vi.fn().mockReturnValue(0),
-			addMemoryUsage: vi.fn(),
+			getTotalMemoryUsed: vi.fn(() => totalMemoryUsed),
+			addMemoryUsage: vi.fn((sizeInMB: number) => {
+				totalMemoryUsed += sizeInMB
+			}),
 		}
 	}),
 	DEFAULT_MAX_IMAGE_FILE_SIZE_MB: 5,
@@ -28,50 +32,154 @@ const mockValidateImage = vi.mocked(validateImageForProcessing)
 describe("resolveImageMentions", () => {
 	beforeEach(() => {
 		vi.clearAllMocks()
+		mockReadImageAsDataUrl.mockReset()
+		mockValidateImage.mockReset()
 		// Default: validation passes
 		mockValidateImage.mockResolvedValue({ isValid: true, sizeInMB: 0.1 })
 	})
 
-	it("should append a data URL when a local png mention is present", async () => {
-		const dataUrl = `data:image/png;base64,${Buffer.from("png-bytes").toString("base64")}`
-		mockReadImageAsDataUrl.mockResolvedValue({ dataUrl, buffer: Buffer.from("png-bytes") })
+	it.each([
+		["png", "image/png"],
+		["PNG", "image/png"],
+		["jpg", "image/jpeg"],
+		["jpeg", "image/jpeg"],
+		["gif", "image/gif"],
+		["webp", "image/webp"],
+	])("should append a supported %s image mention", async (extension, mimeType) => {
+		const buffer = Buffer.from("image-bytes")
+		const dataUrl = `data:${mimeType};base64,${buffer.toString("base64")}`
+		mockReadImageAsDataUrl.mockResolvedValue({ dataUrl, buffer })
+		const text = `Please look at @/assets/cat.${extension}`
 
 		const result = await resolveImageMentions({
-			text: "Please look at @/assets/cat.png",
+			text,
 			images: [],
 			cwd: "/workspace",
 		})
 
 		expect(mockValidateImage).toHaveBeenCalled()
-		expect(mockReadImageAsDataUrl).toHaveBeenCalledWith(path.resolve("/workspace", "assets/cat.png"))
-		expect(result.text).toBe("Please look at @/assets/cat.png")
+		expect(mockReadImageAsDataUrl).toHaveBeenCalledWith(path.resolve("/workspace", `assets/cat.${extension}`))
+		expect(result.text).toBe(text)
 		expect(result.images).toEqual([dataUrl])
+		expect(formatResponse.imageBlocks(result.images)).toEqual([
+			{
+				type: "image",
+				source: { type: "base64", media_type: mimeType, data: buffer.toString("base64") },
+			},
+		])
 	})
 
-	it("should support gif images (matching read_file)", async () => {
-		const dataUrl = `data:image/gif;base64,${Buffer.from("gif-bytes").toString("base64")}`
-		mockReadImageAsDataUrl.mockResolvedValue({ dataUrl, buffer: Buffer.from("gif-bytes") })
+	it.each([
+		["svg", "image/svg+xml"],
+		["bmp", "image/bmp"],
+		["ico", "image/x-icon"],
+		["tiff", "image/tiff"],
+		["tif", "image/tiff"],
+		["avif", "image/avif"],
+	])("should skip %s mentions with unsupported MIME types", async (extension, mimeType) => {
+		const buffer = Buffer.from("unsupported-image-bytes")
+		const dataUrl = `data:${mimeType};base64,${buffer.toString("base64")}`
+		mockReadImageAsDataUrl.mockResolvedValue({ dataUrl, buffer })
+		const text = `See @/image.${extension}`
 
 		const result = await resolveImageMentions({
-			text: "See @/animation.gif",
+			text,
 			images: [],
 			cwd: "/workspace",
 		})
 
-		expect(result.images).toEqual([dataUrl])
+		expect(result.text).toBe(text)
+		expect(result.images).toEqual([])
+		expect(formatResponse.imageBlocks(result.images)).toEqual([])
+	})
+
+	it.each(["not-a-data-url", "data:;base64,aW1hZ2U="])(
+		"should skip image data URLs without a recognized MIME type: %s",
+		async (dataUrl) => {
+			mockReadImageAsDataUrl.mockResolvedValue({ dataUrl, buffer: Buffer.from("image-bytes") })
+
+			const result = await resolveImageMentions({
+				text: "See @/image.png",
+				images: [],
+				cwd: "/workspace",
+			})
+
+			expect(result.images).toEqual([])
+		},
+	)
+
+	it("should preserve existing images and supported mentions when unsupported mentions are mixed in", async () => {
+		const buffer = Buffer.from("image-bytes")
+		const base64 = buffer.toString("base64")
+		const existingImage = `data:image/png;base64,${base64}`
+		const supportedImage = `data:image/webp;base64,${base64}`
+		mockReadImageAsDataUrl
+			.mockResolvedValueOnce({ dataUrl: `data:image/svg+xml;base64,${base64}`, buffer })
+			.mockResolvedValueOnce({ dataUrl: supportedImage, buffer })
+			.mockResolvedValueOnce({ dataUrl: `data:image/bmp;base64,${base64}`, buffer })
+		const text = "Compare @/icon.svg, @/photo.webp and @/bitmap.bmp"
+
+		const result = await resolveImageMentions({
+			text,
+			images: [existingImage],
+			cwd: "/workspace",
+		})
+
+		expect(mockReadImageAsDataUrl).toHaveBeenCalledTimes(3)
+		expect(result.text).toBe(text)
+		expect(result.images).toEqual([existingImage, supportedImage])
+		expect(formatResponse.imageBlocks(result.images)).toHaveLength(2)
 	})
 
-	it("should support svg images (matching read_file)", async () => {
-		const dataUrl = `data:image/svg+xml;base64,${Buffer.from("svg-bytes").toString("base64")}`
-		mockReadImageAsDataUrl.mockResolvedValue({ dataUrl, buffer: Buffer.from("svg-bytes") })
+	it("should not count unsupported image mentions toward the total memory limit", async () => {
+		mockValidateImage.mockImplementation(
+			async (_filePath, _supportsImages, _maxImageFileSize, maxTotalImageSize, currentTotalMemoryUsed) => ({
+				isValid: currentTotalMemoryUsed + 10 <= maxTotalImageSize,
+				sizeInMB: 10,
+			}),
+		)
+		const buffer = Buffer.from("image-bytes")
+		const base64 = buffer.toString("base64")
+		const firstSupportedImage = `data:image/png;base64,${base64}`
+		const secondSupportedImage = `data:image/jpeg;base64,${base64}`
+		mockReadImageAsDataUrl
+			.mockResolvedValueOnce({ dataUrl: `data:image/svg+xml;base64,${base64}`, buffer })
+			.mockResolvedValueOnce({ dataUrl: firstSupportedImage, buffer })
+			.mockResolvedValueOnce({ dataUrl: secondSupportedImage, buffer })
 
 		const result = await resolveImageMentions({
-			text: "See @/icon.svg",
+			text: "See @/icon.svg, @/first.png and @/second.jpg",
 			images: [],
 			cwd: "/workspace",
+			maxImageFileSize: 10,
+			maxTotalImageSize: 20,
 		})
 
-		expect(result.images).toEqual([dataUrl])
+		expect(result.images).toEqual([firstSupportedImage, secondSupportedImage])
+		expect(mockValidateImage).toHaveBeenNthCalledWith(2, path.resolve("/workspace", "first.png"), true, 10, 20, 0)
+		expect(mockValidateImage).toHaveBeenNthCalledWith(3, path.resolve("/workspace", "second.jpg"), true, 10, 20, 10)
+	})
+
+	it("should not count unsupported image mentions toward the image count limit", async () => {
+		const existingImages = Array.from(
+			{ length: 19 },
+			(_, index) => `data:image/png;base64,${Buffer.from(`existing-${index}`).toString("base64")}`,
+		)
+		const buffer = Buffer.from("new-image-bytes")
+		const base64 = buffer.toString("base64")
+		const supportedImage = `data:image/png;base64,${base64}`
+		mockReadImageAsDataUrl
+			.mockResolvedValueOnce({ dataUrl: `data:image/svg+xml;base64,${base64}`, buffer })
+			.mockResolvedValueOnce({ dataUrl: supportedImage, buffer })
+
+		const result = await resolveImageMentions({
+			text: "See @/icon.svg, @/last.png and @/over-limit.jpg",
+			images: existingImages,
+			cwd: "/workspace",
+		})
+
+		expect(result.images).toEqual([...existingImages, supportedImage])
+		expect(mockReadImageAsDataUrl).toHaveBeenCalledTimes(2)
 	})
 
 	it("should ignore non-image mentions", async () => {
diff --git a/src/core/mentions/resolveImageMentions.ts b/src/core/mentions/resolveImageMentions.ts
index 0a0344348f..b4b905c5c2 100644
--- a/src/core/mentions/resolveImageMentions.ts
+++ b/src/core/mentions/resolveImageMentions.ts
@@ -1,6 +1,7 @@
 import * as path from "path"
 
 import { mentionRegexGlobal, unescapeSpaces } from "../../shared/context-mentions"
+import { getImageMimeType, isSupportedImageMimeType } from "../../utils/imageMime"
 import {
 	isSupportedImageFormat,
 	readImageAsDataUrlWithBuffer,
@@ -50,8 +51,11 @@ function dedupePreserveOrder(values: string[]): string[] {
  * Resolves local image file mentions like `@/path/to/image.png` found in `text` into `data:image/...;base64,...`
  * and appends them to the outgoing `images` array.
  *
- * Behavior matches the read_file tool:
- * - Supports the same image formats: png, jpg, jpeg, gif, webp, svg, bmp, ico, tiff, avif
+ * Recognizes the same image extensions as the read_file tool, but only appends images
+ * supported by the shared image-block contract (JPEG, PNG, GIF, and WebP).
+ * Other image MIME types are skipped without changing the original text.
+ *
+ * Like the read_file tool:
  * - Respects per-file size limits (default 5MB)
  * - Respects total memory limits (default 20MB)
  * - Skips images if model doesn't support them
@@ -128,6 +132,10 @@ export async function resolveImageMentions({
 			}
 
 			const { dataUrl } = await readImageAsDataUrlWithBuffer(absPath)
+			if (!isSupportedImageMimeType(getImageMimeType(dataUrl))) {
+				// Fail-soft: skip formats unsupported by the shared image-block contract.
+				continue
+			}
 			newImages.push(dataUrl)
 
 			// Track memory usage
diff --git a/src/core/prompts/__tests__/responses-images.spec.ts b/src/core/prompts/__tests__/responses-images.spec.ts
new file mode 100644
index 0000000000..c88d76acf7
--- /dev/null
+++ b/src/core/prompts/__tests__/responses-images.spec.ts
@@ -0,0 +1,122 @@
+import { formatResponse } from "../responses"
+import { IMAGE_MIME_TYPES } from "../../tools/helpers/imageHelpers"
+import { getImageMimeType, isSupportedImageMimeType } from "../../../utils/imageMime"
+
+const supportedMimeTypes = ["image/jpeg", "image/png", "image/gif", "image/webp"] as const
+const supportedMimeTypeSet = new Set<string>(supportedMimeTypes)
+const unsupportedMimeTypes = [
+	...new Set([...Object.values(IMAGE_MIME_TYPES), "image/heic", "application/octet-stream", "image/svg+xml"]),
+].filter((mimeType) => !supportedMimeTypeSet.has(mimeType))
+const payload = "c3ludGhldGlj"
+
+describe("image MIME utilities", () => {
+	it.each(supportedMimeTypes)("extracts and accepts the SDK MIME type %s", (mimeType) => {
+		expect(getImageMimeType(`data:${mimeType};base64,${payload}`)).toBe(mimeType)
+		expect(isSupportedImageMimeType(mimeType)).toBe(true)
+	})
+
+	it.each(unsupportedMimeTypes)("extracts but rejects the unsupported MIME type %s", (mimeType) => {
+		expect(getImageMimeType(`data:${mimeType};base64,${payload}`)).toBe(mimeType)
+		expect(isSupportedImageMimeType(mimeType)).toBe(false)
+	})
+
+	it("returns no MIME for a missing header and rejects absent or empty MIME values", () => {
+		expect(getImageMimeType("")).toBeUndefined()
+		expect(isSupportedImageMimeType(undefined)).toBe(false)
+		expect(isSupportedImageMimeType("")).toBe(false)
+	})
+})
+
+describe("shared image-block MIME contract", () => {
+	it.each(supportedMimeTypes)("preserves the complete image block for %s through both entry points", (mimeType) => {
+		const dataUrl = `data:${mimeType};base64,${payload}`
+		const image = { type: "image", source: { type: "base64", media_type: mimeType, data: payload } }
+		expect(formatResponse.imageBlocks([dataUrl])).toEqual([image])
+		expect(formatResponse.toolResult("read result", [dataUrl])).toEqual([
+			{ type: "text", text: "read result" },
+			image,
+		])
+	})
+
+	it.each(unsupportedMimeTypes)("rejects %s through both entry points before returning a payload", (mimeType) => {
+		const dataUrl = `data:${mimeType};base64,${payload}`
+		const error = new Error(`Unsupported image MIME type: ${mimeType}. Use JPEG, PNG, GIF, or WebP.`)
+		expect(() => formatResponse.imageBlocks([dataUrl])).toThrowError(error)
+		expect(() => formatResponse.toolResult("read result", [dataUrl])).toThrowError(error)
+	})
+
+	it.each([
+		"",
+		"not a data URL",
+		"data:;base64,c3ludGhldGlj",
+		"data:image/png,c3ludGhldGlj",
+		"data:image/png;base64",
+		"data:image/png;base64;c3ludGhldGlj",
+		"data:image/png;charset=utf-8;base64,c3ludGhldGlj",
+		"DATA:image/png;base64,c3ludGhldGlj",
+		"data:image/png;BASE64,c3ludGhldGlj",
+		"prefix data:image/png;base64,c3ludGhldGlj",
+		" data:image/png;base64,c3ludGhldGlj",
+		"\uFEFFdata:image/png;base64,c3ludGhldGlj",
+		"data\uFF1Aimage/png;base64,c3ludGhldGlj",
+		"data:image/png;base64\uFF0Cc3ludGhldGlj",
+	])("rejects a malformed or noncanonical header: %j", (dataUrl) => {
+		const error = new Error("Unsupported image MIME type: unknown. Use JPEG, PNG, GIF, or WebP.")
+		expect(() => formatResponse.imageBlocks([dataUrl])).toThrowError(error)
+		expect(() => formatResponse.toolResult("read result", [dataUrl])).toThrowError(error)
+	})
+
+	it.each(["image/PNG", "image/jpg", "image/png ", "image/p\u200Bng", "image/\u0440ng", "image\uFF0Fpng"])(
+		"does not normalize unsupported MIME spelling %j into an allowed type",
+		(mimeType) => {
+			const dataUrl = `data:${mimeType};base64,${payload}`
+			const error = new Error(`Unsupported image MIME type: ${mimeType}. Use JPEG, PNG, GIF, or WebP.`)
+			expect(() => formatResponse.imageBlocks([dataUrl])).toThrowError(error)
+			expect(() => formatResponse.toolResult("read result", [dataUrl])).toThrowError(error)
+		},
+	)
+
+	it.each([{ images: undefined }, { images: [] }])("preserves the no-image response for $images", ({ images }) => {
+		expect(formatResponse.imageBlocks(images)).toEqual([])
+		expect(formatResponse.toolResult("read result", images)).toBe("read result")
+		expect(formatResponse.toolResult("", images)).toBe("")
+	})
+
+	it("preserves image order, duplicate images, Unicode feedback, and the input array", () => {
+		const images = [
+			"data:image/png;base64,Zmlyc3Q=",
+			"data:image/jpeg;base64,c2Vjb25k",
+			"data:image/png;base64,Zmlyc3Q=",
+		]
+		const originalImages = [...images]
+		const expected = [
+			{ type: "image", source: { type: "base64", media_type: "image/png", data: "Zmlyc3Q=" } },
+			{ type: "image", source: { type: "base64", media_type: "image/jpeg", data: "c2Vjb25k" } },
+			{ type: "image", source: { type: "base64", media_type: "image/png", data: "Zmlyc3Q=" } },
+		]
+		const text = "\u041E\u0442\u0432\u0435\u0442 \uD83D\uDDBC\uFE0F e\u0301"
+		expect(formatResponse.imageBlocks(images)).toEqual(expected)
+		expect(formatResponse.toolResult(text, images)).toEqual([{ type: "text", text }, ...expected])
+		expect(images).toEqual(originalImages)
+	})
+
+	it.each([0, 1, 2])("rejects an unsupported image at index %i without changing the input", (index) => {
+		const images = Array<string>(3).fill(`data:image/png;base64,${payload}`)
+		images[index] = `data:image/bmp;base64,${payload}`
+		const originalImages = [...images]
+		const error = new Error("Unsupported image MIME type: image/bmp. Use JPEG, PNG, GIF, or WebP.")
+		expect(() => formatResponse.imageBlocks(images)).toThrowError(error)
+		expect(() => formatResponse.toolResult("read result", images)).toThrowError(error)
+		expect(images).toEqual(originalImages)
+	})
+
+	it.each(["", "not decoded here", "first,second", "\uD83D\uDE00e\u0301"])(
+		"preserves the opaque payload %j without adding byte or base64 validation",
+		(data) => {
+			const dataUrl = `data:image/png;base64,${data}`
+			const image = { type: "image", source: { type: "base64", media_type: "image/png", data } }
+			expect(formatResponse.imageBlocks([dataUrl])).toEqual([image])
+			expect(formatResponse.toolResult("", [dataUrl])).toEqual([{ type: "text", text: "" }, image])
+		},
+	)
+})
diff --git a/src/core/prompts/responses.ts b/src/core/prompts/responses.ts
index 7714438431..d8a3fa4fee 100644
--- a/src/core/prompts/responses.ts
+++ b/src/core/prompts/responses.ts
@@ -3,6 +3,7 @@ import * as path from "path"
 import * as diff from "diff"
 import { RooIgnoreController, LOCK_TEXT_SYMBOL } from "../ignore/RooIgnoreController"
 import { RooProtectedController } from "../protect/RooProtectedController"
+import { getImageMimeType, isSupportedImageMimeType } from "../../utils/imageMime"
 
 export const formatResponse = {
 	toolDenied: () =>
@@ -226,14 +227,19 @@ Otherwise, if you have not completed the task and do not need additional informa
 // to avoid circular dependency
 const formatImagesIntoBlocks = (images?: string[]): Anthropic.ImageBlockParam[] => {
 	return images
-		? images.map((dataUrl) => {
+		? images.map((dataUrl): Anthropic.ImageBlockParam => {
 				// data:image/png;base64,base64string
-				const [rest, base64] = dataUrl.split(",")
-				const mimeType = rest.split(":")[1].split(";")[0]
+				const mimeType = getImageMimeType(dataUrl)
+				if (!isSupportedImageMimeType(mimeType)) {
+					throw new Error(
+						`Unsupported image MIME type: ${mimeType ?? "unknown"}. Use JPEG, PNG, GIF, or WebP.`,
+					)
+				}
+				const base64 = dataUrl.slice(dataUrl.indexOf(",") + 1)
 				return {
 					type: "image",
 					source: { type: "base64", media_type: mimeType, data: base64 },
-				} as Anthropic.ImageBlockParam
+				}
 			})
 		: []
 }
diff --git a/src/utils/imageMime.ts b/src/utils/imageMime.ts
new file mode 100644
index 0000000000..d9f5d684e6
--- /dev/null
+++ b/src/utils/imageMime.ts
@@ -0,0 +1,18 @@
+import type { Anthropic } from "@anthropic-ai/sdk"
+
+export function getImageMimeType(dataUrl: string): string | undefined {
+	return /^data:([^;]+);base64,/.exec(dataUrl)?.[1]
+}
+
+/**
+ * All providers consume the shared Anthropic image-block contract. Since model
+ * capabilities expose only supportsImages, conservatively use its four MIME
+ * types rather than assuming provider-specific support for other encodings.
+ */
+export function isSupportedImageMimeType(
+	mimeType: string | undefined,
+): mimeType is Anthropic.Base64ImageSource["media_type"] {
+	return (
+		mimeType === "image/jpeg" || mimeType === "image/png" || mimeType === "image/gif" || mimeType === "image/webp"
+	)
+}