check if avatar/gravatar is valid(exists)
function validate_gravatar($email) {
// From http://codex.wordpress.org/Using_Gravatars
// Craft a potential url and test its headers
$hash = md5($email);
$uri = 'http://www.gravatar.com/avatar/' . $hash . '?d=404';
$headers = @get_headers($uri);
if (!preg_match("|200|", $headers[0])) {
$has_valid_avatar = FALSE;
} else {
$has_valid_avatar = TRUE;
}
return $has_valid_avatar;
}