Verify a capture

A screenshot made with FullPage Capture's Evidence mode carries the page address, the exact time of the capture and a SHA-256 checksum of its pixels, on the picture and inside the file. Drop the file here to read those facts and check that the picture has not changed since.

Drop a PNG or PDF here, or click to choose oneYour file never leaves this browser: it is read and checked right here.

Check a file without this page

The checksum is SHA-256 over the RGB bytes of the picture above the band, row by row. For a PNG, with Python and Pillow (the band height is printed in the evidence data and shown above):

python3 -c "import hashlib,sys; from PIL import Image
im=Image.open(sys.argv[1]).convert('RGB'); w,h=im.size; b=int(sys.argv[2])
print(hashlib.sha256(im.crop((0,0,w,h-b)).tobytes()).hexdigest())" capture.png 156

A PDF holds one lossless image per page (the object named /Im0, Flate with PNG's Up predictor); the checksum runs over those images in page order. The evidence data itself is the /FPC_Evidence entry of the PDF's Info dictionary, and the fpc:evidence text chunk of a PNG.