Gravatar is one of the most common used service used widely on WordPress blogging platform. Gravatar is used for providing globally unique avatar for a specific email. During advance WordPress development, you may want to check if Gravatar is available for a users email, to display image or avatar from alternative source.
The following PHP snippets can be used to determine if Gravatar is available for specified email. It returns TRUE for valid gravatar otherwise it returns false.
Check out the source code in github