select random images for Gravatars

burt-gravatar.php

add_filter ( 'get_avatar', 'rkv_burt_avatar', 10, 5 );

function rkv_burt_avatar($avatar, $id_or_email, $size, $default, $alt) {
	// we don't want this running anywhere on admin. no real reason.
	if (is_admin() )
        return $avatar;

	// making sure we don't hit any of the avatars in the menu bar or other weird spots    
	if (isset($id_or_email) && $id_or_email !== 1) {
		// commenters
        $email  = $id_or_email->comment_author_email;
        $exist  = rkv_validate_gravatar($email);

	} else {
		// this is for folks with user accounts on the site
	$u_id   = get_current_user_id();
        $email  = get_the_author_meta( 'user_email', $u_id );
        $exist  = true;
	}

	if($exist == true ) {
		$grav_img   = 'http://www.gravatar.com/avatar/'.md5(strtolower($email)) . '?d=' . urlencode($default) . '&s=' . $size;
		$gravatar   = '<img src="'.$grav_img.'"/>';
	} else {
		$burt_img   = gimme_burt();
		$gravatar   = '<img src="'.get_stylesheet_directory_uri().'/images/burt/'.$burt_img.'" height="'.$size.'" width="'.$size.'"/>';
	}
        
	return $gravatar;
}

// function for checking on the existance of a gravatar
function rkv_validate_gravatar($email) {
	// Craft a potential url and test its headers
	$hash		= md5(strtolower(trim($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;
}

// function for scanning the folder with the images to be used
function gimme_burt() {
	$burt_array = scandir( get_stylesheet_directory(__FILE__) . '/images/burt' );
	$burt_faces = array_filter( $burt_array, create_function('$x','return in_array(strtolower(substr($x,-3)),array("png","jpg","gif"));'));
	$burt_face  = array_rand(array_flip($burt_faces), 1);
	
	return $burt_face;
}