Image Compare / Diff Tool

About this tool

Compare two images two ways. The slider lays one image over the other and lets you wipe between them — the quickest way to see what changed between a before and after, two design revisions, or two exports. The pixel diff highlights every changed pixel in red over a dimmed copy of Image A, with a "percent different" score. Both images stay in your browser; nothing is uploaded.

What counts as a different pixel. The diff compares the two images pixel-for-pixel and flags any pixel whose colour differs by more than a small tolerance. The tolerance exists so that JPEG compression noise — which changes almost every pixel by a tiny amount — doesn't light up the whole image. A pixel that moved from pure white to near-white is treated as unchanged; one that changed hue or jumped several shades is flagged.

Size mismatch. A pixel diff only makes sense when both images are the same dimensions. If they differ, Image B is scaled to match Image A first. That scaling distorts B slightly, which can itself register as a band of differences along edges — so the diff is most reliable when the two images are genuinely the same size, such as two screenshots of the same viewport or two exports at the same resolution.

What it's good for. Visual regression checks (did this CSS change move anything unexpected?), spotting a subtle retouch, confirming two "identical" files really are, comparing compression settings, and proofreading a redesign against the original.

What it won't do. It has no understanding of content — a one-pixel shift of the whole layout reads as "almost everything changed," even though nothing meaningful moved. It doesn't align or register images, ignore anti-aliasing intelligently, or tell you what changed, only where.

To find near-duplicate files across a folder rather than compare two specific images, use the duplicate image finder. To change format or compression before comparing, the image format converter and image compressor.

Frequently asked questions

What counts as a "different" pixel in the diff view?

Any pixel whose colour differs from the matching pixel by more than a small tolerance. The tolerance stops JPEG compression noise from flagging the entire image.

Why does resizing Image B affect the result?

Pixel diffing compares images at the same coordinates, so both must be the same size. Scaling B to fit distorts it slightly, and that distortion can show up as differences along edges.

Why does a tiny layout shift show as a huge difference?

The diff has no concept of content or alignment. If everything moves one pixel, every pixel is "different" even though nothing meaningful changed.

Is either image uploaded anywhere?

No. Both the slider and the pixel diff render entirely in your browser.

Can it compare two PDFs or two web pages?

Not directly — it works on image files. Export each page or screenshot to PNG at the same size first.

Does it show which image is "newer" or "correct"?

No. It only shows where they differ. You decide which is the reference.