An identicon is a little icon used to identify the contributions of an individual user across websites, blogs and wikis.
Identicons provide visual cues, so you can immediately recognize the comments of your friends in a lengthy discussion thread, or notice that a new person has joined the party.
You can use identicons via k2g2's identicon plugin.
The same identicon is used across all websites supporting the identicon service, so it must be possible to
Most forums, blogs and websites ask their users to identify themselves by giving an email address (mostly for legal reasons). This information is used as a unique user ID.
A user icon can either be hosted by a global service, or can be locally generated according to a generative algorithm.
Each user can upload an icon of her choice to a global identicon server. Each website can then retrieve or include icons from this server, by transmitting the user IDs.
The user ID contains information, which can be used to generate a unique icon. In compositional identicons, a couple of preconfigured components are combined to form the icon. Generative identicons use a generative algorithm, where the information contained in the user ID serves as a seed from which the icon is grown.
Since email addresses are confidential information, they should not be disclosed. To achieve this, the email address is encrypted by MD5 to form the actual user ID.
Identicons work very much like a written signature. They can be forged, but it's not that simple. Only persons, who know the email address that you use in conjunction with the identicon service may forge your signature. This could be anyone who runs a blog with a local identicon service, all your email contacts or the whole world, if you have published this email address online. When you use a central identicon service, others could also cause confusion by uploading an icon similar or identical to the one you use.