{identicon} gives every account a picture of its own without asking for one: a symmetric pattern on a 5 by 5 grid and a colour, both taken from a SHA-256 hash of the value (tags/_lib/identicon.php). Nothing leaves the server, and the same value is always the same picture.

The value is trimmed and lower-cased before it is hashed, so every spelling of an e-mail address is one picture. Fifteen nibbles of the hash fill the left three columns, mirrored to the right; the colour is a hue from the last bytes at a saturation and lightness that read on the light square behind it, --pad-identicon-background on .pad-identicon (a light-dark() default, written once per page).

Unlike {avatar} the picture says nothing of the value: the accessible name is Identicon, or title, never the address itself. An empty value is an error under the strict check.