Canvas fingerprinting asks your browser to draw text and shapes on an invisible canvas, then reads the resulting pixels. The picture looks the same to the eye, but its exact pixel values depend on your device.
Why pixels differ
- Fonts and how the system smooths text edges
- The graphics card and driver used to draw
- Operating system text and image libraries
- Display settings such as pixel ratio
What a canvas hash tells a website
On its own a canvas hash is not unique, since many people with similar devices share it. Combined with other signals it helps narrow a browser down, and it usually stays stable between visits.
Does blocking help?
Some browsers add small random changes or ask before giving canvas data to a site. This can protect you, but a value that changes on every read can itself be noticeable.