Font fingerprinting techniques rely on measuring the dimensions of HTML elements filled with text or single Unicode glyphs. However, font rendering in web browsers can be affected by multiple factors, leading to subtle differences in these measurements.
Font metrics measurement is a brute force method that tries different fonts from a large dictionary of known typefaces. By comparing the size of the rendered element to the default values, this method can determine if a font is present on the system.
Unicode glyphs measurement technique uses special Unicode characters with a large font size and default letterforms as a font-family to create fingerprints by hashing the obtained measurement results.