You need to
before you can comment on or make changes to this bug.
See for instance: https://bugs.webkit.org/attachment.cgi?id=106368&action=review
The old/new .pngs are shown on top of each other, which makes it hard to do comparisons. We should show at least an ImageDiff view, or preferably a loupe tool / pixel value examiner.
Something like this would be nice https://github.com/blog/817-behold-image-view-modes.