diff --git a/src/components/PromptBox.tsx b/src/components/PromptBox.tsx
index d08bb79..31785a9 100644
--- a/src/components/PromptBox.tsx
+++ b/src/components/PromptBox.tsx
@@ -54,6 +54,67 @@ interface PromptBoxProps
 	contextPercent?: number | null;
 }
 
+const TARGET_IMAGE_SIZE = 4.5 * 1024 * 1024; // Target slightly under 5 MB
+const MAX_DIMENSION = 4096; // Max width/height
+
+async function compressImage(file: File): Promise<string> {
+	const dataUrl = await readFileAsDataURL(file);
+	if (file.size <= TARGET_IMAGE_SIZE) {
+		return dataUrl;
+	}
+
+	return new Promise((resolve, reject) => {
+		const img = new Image();
+		img.onload = () => {
+			const canvas = document.createElement("canvas");
+			let width = img.width;
+			let height = img.height;
+
+			if (width > MAX_DIMENSION || height > MAX_DIMENSION) {
+				const ratio = Math.min(MAX_DIMENSION / width, MAX_DIMENSION / height);
+				width = Math.round(width * ratio);
+				height = Math.round(height * ratio);
+			}
+
+			canvas.width = width;
+			canvas.height = height;
+			const ctx = canvas.getContext("2d");
+			if (!ctx) {
+				reject(new Error("Failed to get canvas context"));
+				return;
+			}
+			ctx.fillStyle = "white";
+			ctx.fillRect(0, 0, width, height);
+			ctx.drawImage(img, 0, 0, width, height);
+
+			let quality = 0.9;
+			const tryCompress = () => {
+				const result = canvas.toDataURL("image/jpeg", quality);
+				const base64Length = result.length - "data:image/jpeg;base64,".length;
+				const byteSize = Math.round((base64Length * 3) / 4);
+
+				if (byteSize <= TARGET_IMAGE_SIZE) {
+					resolve(result);
+				} else if (quality > 0.1) {
+					quality -= 0.1;
+					tryCompress();
+				} else {
+					console.warn(
+						`Image still exceeds target size (${byteSize} bytes) even at minimum quality. Returning low-quality result.`,
+					);
+					resolve(result);
+				}
+			};
+			tryCompress();
+			img.src = "";
+		};
+		img.onerror = () => {
+			reject(new Error("Failed to load image. The file may be corrupt."));
+		};
+		img.src = dataUrl;
+	});
+}
+
 function readFileAsDataURL(file: File): Promise<string> {
 	return new Promise((resolve, reject) => {
 		const reader = new FileReader();
@@ -254,7 +315,7 @@ export const PromptBox = React.forwardRef<HTMLTextAreaElement, PromptBoxProps>(
 					f.type.startsWith("image/"),
 				);
 				if (imageFiles.length === 0) return;
-				const results = await Promise.all(imageFiles.map(readFileAsDataURL));
+				const results = await Promise.all(imageFiles.map(compressImage));
 				setImagePreviews((prev) => [...prev, ...results]);
 			},
 			[isDisabled],