Use Jetpack Photon with arbitrary URLs

photonify.php

<?php
/* 
 This function allows you to use the Jetpack plugin's Photon CDN for arbitrary images in your theme.
 Add this function to your functions.php, then call it by passing an image url. 
 ex. <img src="<?= photonify(get_template_directory_uri() . /images/logo.png) ?>" alt="company logo"> 
*/


function photonify( $src ) {
	if ( class_exists( 'Jetpack' ) && Jetpack::is_module_active( 'photon' ) ) { 
		$url = parse_url( $src );
		// it's relative, add the host
	  	if ( !isset($url['host']) ) {
	  		$hostname = $_SERVER['HTTP_HOST']; 
	  		$url = 'http://'.$hostname.$src;
	  	} else {
			$url = $src;
		}
	  	return apply_filters( 'jetpack_photon_url', $url );
	}
	
	return $src;
}
?>