Installed fonts: to detect system fonts, tracking sites typically render text inside an HTML <span> and rapidly iterate styles across hundreds or thousands of known fonts. For each font the site checks whether the element’s width changed compared with the default when rendered in that font. If it did, the tracker concludes the font is installed. The list of fonts present on your machine is often consistent and tied to a particular operating system. If you have installed even a single uncommon font (for example a designer font), that can be a highly informative metric.
Cookie support: the metric “cookies enabled” can be either True or False, indicating whether your browser allows cookies or blocks them. Cookie support can be detected with JavaScript or without it. Alone this provides just one bit of information — True or False — but it becomes much more informative when combined with other attributes.
Supercookie detection: despite the name, “supercookies” are not technically cookies. Although they also store and retrieve unique identifiers, they are much harder to detect and remove. Supercookies can track which sites you visit and how long you spend on them. They can also access data gathered by traditional tracking cookies, for example login information. After a standard cookie is deleted, a supercookie can still reference it.
Language settings: the browser’s preferred language(s). This metric indicates which languages you prefer to see website content in. It adds substantial information to a fingerprint, especially if the language is uncommon in your time zone.
Canvas and WebGL fingerprinting: WebGL and Canvas fingerprint results are closely related. Both methods examine graphics rendered by the browser for minute differences between users. This is a sophisticated and highly reliable fingerprinting metric. Rendered images will slightly differ due to small variances in: GPU hardware, graphics drivers, the operating system and installed fonts. These settings vary across machines, but are typically stable enough on a single machine to uniquely identify a user.
