Two photographs of the same scene differ in almost every pixel because of camera grain and JPEG compression. Slide Sensitivity to the right until only the real edits remain. Screenshots and exported images, which have no grain, work well at a low setting.
Slide Sensitivity to the left. Very faint edits — a slight colour shift, antialiasing on a moved edge — sit below the default threshold on purpose, so that noise does not drown the result.
That is fine. PixelSpot scales them to match before comparing and tells you it did. Bear in mind that scaling a photo shifts its pixels slightly, so expect a few extra findings around edges.
If the two images really are identical files, PixelSpot says so. If you expected a difference, check that you picked two different images — the thumbnails at the top show which are loaded.
Comparisons run at up to 1600 pixels on the long edge. Beyond that the extra detail makes no visible difference to the result and would cost several seconds, so larger images are scaled down first.
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