Gravatar is a service for providing globally unique avatars and was created by Tom Preston-Werner. Since 2007, it has been owned by Automattic, having integrated it into their WordPress.com blogging platform.
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On Gravatar, users can register an account based on their email address, and upload a digital avatar to be associated with the account. Gravatar plugins are available for popular blogging software; when the user posts a comment on such a blog that requires an email address, the blogging software checks whether that email address has an associated avatar at Gravatar. If so, the Gravatar is shown along with the comment. Gravatar support is provided natively in WordPress as of v2.5 and in web based project management applicationRedmine beginning with version 0.8. Support for Gravatar is also provided via third-party modules for web content management systems such as Drupal and MODX. A Gravatar image can be up to 2048 pixels wide, is always square and is displayed at 80 by 80 pixels by default. If the uploaded avatar is larger or smaller, the avatar is scaled appropriately. Each Gravatar is rated with an MPAA-style age recommendation, allowing webmasters to control the content of the Gravatars displayed on their website. Webmasters can also configure their system to automatically display an Identicon when a user has no registered Gravatar. Gravatars are loaded from the Gravatar web server, using a URL containing an MD5 hash of the associated email address. This method has, however, been shown to be vulnerable to dictionary attacks and rainbow table approaches.
For some time, the Gravatar service remained unmaintained. The maker became busy with working on a new version of the service, as Gravatar's popularity grew and more bandwidth was required. On 16 February 2007, "Gravatar 2.0" was launched. Besides an improved server script, users also noticed other improvements, such as being able to crop and use an image already hosted on the web. Support for two gravatars per account was added, between which the user can easily switch. "Gravatar Premium" was also launched, allowing unlimited email addresses and Gravatars per account. On 11 June 2007, Tom Preston-Werner announced that 32,000 new users had signed up since the launch of Gravatar 2.0. On 18 October 2007, Automattic acquired Gravatar. After doing so, they offered all previously paid services at no cost, improved server response time, and refunded those who had recently paid for service. Matt Mullenweg announced on The Big Web Show on 2 December 2010 that Gravatar was serving approximately 20 billion images per day.
