Status Machine creates what we call a “visual difference” between 2 snapshots. What it does is that for every page in the snapshot that you created, we take the screenshots, and compare them to the other snapshot you’re comparing to.
As for detecting those visual differences, every pixel of the screenshots are compared to the homologous screenshots of the compared snapshot, and if the pixels are different, they are marked as such. And a map (a resulting image) of the different pixels is generated for those pages. This map is the visual difference for a single page, where all the different pixels are in red, and everything else is white.
In the visual comparison view of Status Machine, this image is useful for quickly spotting differences found in a given page, between two snapshots.