How This Image Diff Tool Works
Upload two images, and this image diff online tool compares them automatically, no button to press, the comparison updates the moment both images are loaded. It's a genuine pixel comparison tool, every pixel in image A is checked against the same position in image B, with changed areas highlighted in red directly on the diff overlay.
Adjustable Threshold for Exact or Lenient Comparison
A threshold slider controls how large a color difference counts as a change, at zero this becomes a strict image comparison tool free of any tolerance, flagging even a single-value difference in any color channel. Raise it and this screenshot diff tool becomes more lenient, useful for ignoring minor compression artifacts or anti-aliasing noise between two otherwise-identical screenshots, so you can find differences between two images that actually matter rather than pixel-level rounding noise.
Handling Different Image Sizes
When the two images do not share the same dimensions, this image diff checker still runs, the smaller image is padded with transparency to match the larger one's canvas size before comparing, and a warning explains what happened. This means you can compare images side by side online even when a redesign changed the canvas size, though the padded area will always show as a difference since there is nothing to compare it against.
Common Uses and Limitations
A common reason to reach for a visual regression testing tool online like this is checking whether a UI change altered more of a screenshot than intended, comparing a design mockup against a shipped implementation, or playing spot the difference tool online with two versions of an image. This tool compares raw pixel values only, it has no perceptual or structural similarity scoring and does not align or register shifted content, if the second image is the same scene shifted by even one pixel, every pixel will register as different.