source/php/Entity/PostManager.php
private function attachmentExists($src)
    {
        global $wpdb;
        $query = "SELECT ID FROM {$wpdb->posts} WHERE guid = '$src'";
        $id = $wpdb->get_var($query);

        if (!empty($id) && $id > 0) {
            return $id;
        }

        return false;
    }
private function attachmentExists($src)
    {
        global $wpdb;
        $query = "SELECT ID FROM {$wpdb->posts} WHERE guid = '$src'";
        $id = $wpdb->get_var($query);

        if (!empty($id) && $id > 0) {
            return $id;
        }

        return false;
    }
Checks if a attachment src already exists in media library
@param  string $src Media url
@return mixed