Get the Attachment ID from an Image URL in WordPress

aa_URLtoAttachmentID.php

function pn_get_attachment_id_from_url( $attachment_url = '' ) {
 
	global $wpdb;
	$attachment_id = false;
 
	// If there is no url, return.
	if ( '' == $attachment_url )
		return;
 
	// Get the upload directory paths
	$upload_dir_paths = wp_upload_dir();
 
	// Make sure the upload path base directory exists in the attachment URL, to verify that we're working with a media library image
	if ( false !== strpos( $attachment_url, $upload_dir_paths['baseurl'] ) ) {
 
		// If this is the URL of an auto-generated thumbnail, get the URL of the original image
		$attachment_url = preg_replace( '/-\d+x\d+(?=\.(jpg|jpeg|png|gif)$)/i', '', $attachment_url );
 
		// Remove the upload path base directory from the attachment URL
		$attachment_url = str_replace( $upload_dir_paths['baseurl'] . '/', '', $attachment_url );
 
		// Finally, run a custom database query to get the attachment ID from the modified attachment URL
		$attachment_id = $wpdb->get_var( $wpdb->prepare( "SELECT wposts.ID FROM $wpdb->posts wposts, $wpdb->postmeta wpostmeta WHERE wposts.ID = wpostmeta.post_id AND wpostmeta.meta_key = '_wp_attached_file' AND wpostmeta.meta_value like '%s' AND wposts.post_type = 'attachment'", '%'.$attachment_url.'%' ) );
 
	}
 
	return $attachment_id;
}