Get all posts (of any post type) an attachment is used in

Second pass. Known issues:

• Needs caching (and the cache needs to be tidied up where possible)
• Post types are hard-coded
• Which post statuses are we interested in?

Here’s the function:

/**
 * Given an attachment ID, searches for any post with that attachment used
 * as a featured image, or if it is present in the content of the post.
 * (Note above known issues).
*/
function get_image_count( $id ){
    global $wpdb;

    $att  = get_post_custom( $id );
    $file = $att['_wp_attached_file'][0];
    //Do not take full path as different image sizes could
    // have different month, year folders due to theme and image size changes
    $file = sprintf( "%s.%s",
        pathinfo( $file, PATHINFO_FILENAME ),
        pathinfo( $file, PATHINFO_EXTENSION )
    );

    $sql = "SELECT {$wpdb->posts}.ID 
        FROM {$wpdb->posts} 
        INNER JOIN {$wpdb->postmeta} 
        ON ({$wpdb->posts}.ID = {$wpdb->postmeta}.post_id) 
        WHERE {$wpdb->posts}.post_type IN ('post', 'page', 'event') 
        AND (({$wpdb->posts}.post_status="publish")) 
        AND ( ({$wpdb->postmeta}.meta_key = '_thumbnail_id' 
            AND CAST({$wpdb->postmeta}.meta_value AS CHAR) = '%d') 
            OR ( {$wpdb->posts}.post_content LIKE %s )
        ) 
        GROUP BY {$wpdb->posts}.ID";

    $prepared_sql = $wpdb->prepare( $sql, $id, "%src=\"%".$wpdb->esc_like( $file )."\"%" );

    $post_ids  = $wpdb->get_results( $prepared_sql );

    $count = count( $post_ids );

    return $count;
}