The four views, and when each helps
Highlight changes fades the first image to near-white and burns every changed pixel through it in red. It is the one to start with: a two-pixel shift in a button is invisible side by side and unmissable here.
Raw difference shows the arithmetic difference per channel, which is useful when you want to see how something changed rather than just where. Fade and Swipe are for judging by eye — alignment, spacing, colour — where a pixel count says nothing useful.
Tolerance
Two screenshots of the same page can differ by a shade or two from antialiasing and JPEG artefacts, which floods the highlight view with noise. Tolerance sets how far a channel may drift before it counts. Zero catches everything; the default of 12 ignores compression noise while still catching a real change.
Images of different sizes
Nothing is scaled to fit. Scaling would resample every pixel and invent differences that were never there. The overlapping area is compared as-is, the rest is counted as changed, and the tool tells you that is what happened.
Frequently asked questions
Are my images uploaded anywhere?
No. Everything runs in your browser with JavaScript. Nothing is uploaded, and the tool keeps working with the network off.
It says 100% differs but they look the same.
Check the size note. If the two images are different dimensions, everything outside the overlap counts as changed. It can also mean one has an alpha channel and the other does not.
Can I compare more than two?
Not at once. Compare them in pairs — with three images the interesting question is usually which pair differs anyway.
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