Frizzly Patch

<?php
/**
	 * Function copied from http://frankiejarrett.com/get-an-attachment-id-by-url-in-wordpress/
	 * Return an ID of an attachment by searching the database with the file URL.
	 *
	 * First checks to see if the $url is pointing to a file that exists in
	 * the wp-content directory. If so, then we search the database for a
	 * partial match consisting of the remaining path AFTER the wp-content
	 * directory. Finally, if a match is found the attachment ID will be
	 * returned.
	 *
	 * @return {int} $attachment
	 */
	private static function fjarrett_get_attachment_id_by_url( $url ) {

		// Split the $url into two parts with the wp-content directory as the separator.
		$parse_url = explode( parse_url( WP_CONTENT_URL, PHP_URL_PATH ), $url );

		// Get the host of the current site and the host of the $url, ignoring www.
		$this_host = str_ireplace( 'www.', '', parse_url( home_url(), PHP_URL_HOST ) );
		$file_host = str_ireplace( 'www.', '', parse_url( $url, PHP_URL_HOST ) );

		// Return nothing if there aren't any $url parts or if the current host and $url host do not match.
		if ( ! isset( $parsed_url[1] ) || empty( $parsed_url[1] ) || ( $this_host != $file_host ) ) {
			return;
		}

		// Now we're going to quickly search the DB for any attachment GUID with a partial path match.
		// Example: /uploads/2013/05/test-image.jpg
		global $wpdb;

		$attachment = $wpdb->get_col( $wpdb->prepare( "SELECT ID FROM $wpdb->posts WHERE post_type = 'attachment' AND guid LIKE %s", $parsed_url[1] ) );
		if ( is_array( $attachment ) && ! empty( $attachment ) ) {
			return array_shift( $attachment );
		}

		return null;
	}

Improve performance on query. Check only post_type attachment ;)

Why not use attachment_url_to_postid ? I'm not sure if you can rely on guid anymore.