Glossary

Canvas fingerprinting

A technique that makes the browser draw hidden text and shapes and reads back the image. Small differences in fonts, graphics drivers and hardware turn the result into a stable identifier of the device.

Also called: canvas fingerprint, canvas hash.

The drawing happens in the background and the user never sees it. Castle, a bot detection company, describes canvas fingerprints as "quite unique and stable," which is why sites use them to recognize returning devices even after cookies are deleted.

Antidetect browsers change it per profile, usually by adding slight noise to the image so each profile's hash differs. Detectors answer with a proof of work: they draw something with known colors and check specific pixels, so the noise shows up as values that are off. Castle's own summary is that "There are no silver bullets to detect if a canvas has been artificially modified," so detectors combine several checks.

For a profile, the safest canvas stays the same between visits and comes from the antidetect's own engine settings, not from an extra browser extension, because extensions leave traces a script can find.