|Type of site||Avatar hosting|
|Created by||Tom Preston-Werner|
|Alexa rank||1,536 (August 2012[update])|
On Gravatar, users can register an account based on their email address, and upload an 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 e-mail address, the blogging software checks whether that e-mail 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 Redmine web based project management application beginning with version 0.8 (2008-12-07). Support for Gravatars is also provided via a third party module in the Drupal web content management system.
A Gravatar avatar 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, which allows 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.
To eliminate spam, e-mail addresses are hashed with the MD5 cryptographic hash function. This prevents spambots from harvesting e-mail addresses. However, Gravatars have been shown to be vulnerable to dictionary attacks (in one real-life example over 10% of the e-mail addresses of a set of forum users were recovered from the Gravatars combined with the forum user names) and rainbow table approaches.
User's profile data is available in a number of metadata standards, including hCard, JSON, XML, PHP, and vCard as well as via QR Codes. The raw data formats (JSON, XML, PHP) use the Portable Contacts standard.
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 Internet. Support for two gravatars per account was added, between which the user can easily switch. "Gravatar Premium" was also launched, which allows unlimited e-mail addresses and Gravatars per account.
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.
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