From Seo Wiki - Search Engine Optimization and Programming Languages
An Identicon is a visual representation of a hash value, usually of the IP address, serving to identify a user of a computer system. The original Identicon is a 9-block graphic, which has been extended to other graphic forms by third parties some of whom have used MD5 instead of the IP address as the identifier. In summary, an Identicon is a privacy protecting derivative of each user's IP address built into a 9-block image and displayed next the user's name. A visual representation is thought to be easier to compare than one which uses only numbers and more importantly, it maintains the person's privacy. The Identicon graphic is unique since it's based on the user's IP, but it is not possible to recover the IP by looking at the Identicon.
Don Park came up with the Identicon idea on January 18, 2007. Don says, "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." 
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 the IP addresses would generate different Identicons.
- Identicons are used to identify 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."
- ↑ Don Park's Daily Habit at the Internet Archive
- ↑ Munnin [ Product - Identicon ] Quick seller identification in the item listing
- ↑ "Indenticon-based anti-phishing protection". http://www.docuverse.com/blog/donpark/2007/01/22/identicon-based-anti-phishing-protection. "In a roundabout way, it's related to my idea of using DRM to protect one-time passwords but very different once it hatched."