Load a photo of the disc before and after. The page finds the three black dots, lines the two photos up, and compares the black and white bead pattern region by region.
Before
No photo
Drop a photo here or choose one below
Drag a marker if it isn't centred on its dot.
After
No photo
Drop a photo here or choose one below
Drag a marker if it isn't centred on its dot.
Waiting for two photos
–Regions matching
–Median similarity
–Regions compared
–Alignment
Before, alignedAfter, alignedHover a red square to zoom in.samechanged
Each square is a patch of beads. It counts as matching when its similarity is at least 0.5 after allowing a small shift.
Unchanged means at least 70% of patches match. Below 30% means the beads have moved. Anything between is flagged as unclear: retake the photos straight on, without glare.
Alignment uses the three dots first, then corrects for camera tilt using the beads themselves (the dots sit on the rim, higher than the beads, so tilting the camera shifts them differently). “Dots only” means the beads had too little in common to lock onto, which usually means they moved.
The markers are colour-coded: the top dot sits opposite the shortest side of the triangle, so photos can be taken at any rotation.