The Photon module resizes your site’s images on the fly, without cropping them. However, in some cases you might want Photon to apply a custom cropping when resizing certain images.

In the following example, we will use photon to serve Post thumbnails with custom cropping, and use a different cropping on single pages:

if( function_exists( 'jetpack_photon_url' ) ) {
    add_filter( 'jetpack_photon_url', 'jetpack_photon_url', 10, 3 );
}
function jeherve_display_custom( $content, $post ) {

	global $post;

	// If you didn't define a post thumnail, let's forget about all this
	if ( !has_post_thumbnail( $post->ID ) )
		return $content;

	// What's the cropping and the size of image we should use on Single pages?
	// See http://developer.wordpress.com/docs/photon/api/#crop for parameters
	if ( is_single() ) {
		$args = array(
		    'crop'   => '50,50,200px,200px',
		);
	}
	// resizing on other pages
	else {
		$args = array(
		    'resize'   => '200,400',
		);
	}

	// Let's create a Photon Image URL from the Post Thumbnail
	$feat_image_url = wp_get_attachment_image_src( get_post_thumbnail_id($post->ID), 'full');
	$photon_image_url = jetpack_photon_url( $feat_image_url[0], $args );

	// Let's build the image tag
	$our_image = sprintf( '<div class="post-media"><a class="featured-image" href="%1$s" title="%2$s"><img src="%3$s" class="wp-post-image" alt="Featured Image"></a></div>',
		esc_url( get_permalink() ),
		esc_attr( sprintf( __( 'Open %s', 'dot' ), get_the_title() ) ),
		esc_attr( $photon_image_url )
	);

	// Let's return the image, right before the post content
	return $our_image . $content;

}
add_filter( 'the_content', 'jeherve_display_custom' );

Reference