An Identicon is a visual representation of a hash value, usually of an IP address, that serves to identify a user of a computer system as a form of avatar while protecting the users' privacy. The original Identicon was a 9-block graphic, and the representation has been extended to other graphic forms by third parties.
Don Park came up with the Identicon idea on January 18, 2007. In his words:
I originally came up with this idea to be used as an easy means of visually distinguishing multiple units of information, anything that can be reduced to bits. It's not just IPs but also people, places, and things. IMHO, too much of the web what we read are textual or numeric information which are not easy to distinguish at a glance when they are jumbled up together. So I think adding visual identifiers will make the user experience much more enjoyable.—Don Park, 
The original Identicon source package 0.1 was server-side Java. Version 0.2 was cleaned up, added some documentation, fixed a color bug, added a cache, and a runtime jar. Version 0.3 included client-side Canvas tags. The current version is 0.5.
- One use is embedding them in wiki pages and blog comments to identify authors. The thought includes protecting an author from someone else using his name to comment. It would be obvious because, in those cases where the ISPs provide unique instead of dynamic IPs, the IP addresses would generate different Identicons.
- Third-party software is available to generate identicons for the purposes of identifying eBay sellers.
- The original Identicon idea has been expanded to include a couple of new, simple yet very effective, anti-phishing protection schemes. One of them requires client-side support; Park is interested in talking to browser vendors regarding its incorporation. He calls this expansion "Gemini."
- An Add-On for Firefox called IdentFavIcon that, on web pages without favicons, replaces them in the tab with Identicons based on the IP of the page.
- Don Park's Daily Habit at the Wayback Machine (archived July 3, 2008)
- The Vash
- Visual Hash Turns Text Or Data Into Abstract Art. Slashdot.
- Munnin [ Product - Identicon ] Quick seller identification in the item listing
- Identicon-based anti-phishing protection at the Wayback Machine (archived May 10, 2008)