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
$attachment_url = preg_replace( ‘/-d+xd+(?=.(jpg|jpeg|png|gif)$)/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 = ‘%s’ AND wposts.post_type = ‘attachment'”, $attachment_url ) );
}
return $attachment_id;
}