Something

/* Checks if the supplied md5 file hash is currently recorded inside of the database, attached to a non-deleted post */
function check_md5($md5, $board) {
    global $tc_db;

    $results = $tc_db->GetAll("SELECT COUNT(*) FROM `".TC_DBPREFIX."posts_".mysql_real_escape_string($board)."` WHERE `imagemd5` = '".mysql_real_escape_string($md5)."' AND `IS_DELETED` = 0 LIMIT 1");
    if ($results[0][0]>0) {
        $results = $tc_db->GetAll("SELECT `id`, `threadid` FROM `".TC_DBPREFIX."posts_".mysql_real_escape_string($board)."` WHERE `imagemd5` = '".mysql_real_escape_string($md5)."' AND `IS_DELETED` = 0 LIMIT 1");
        /* We want the first (and only) row */
        $results = $results[0];
        $real_threadid = ($results[1]==0) ? $results[0] : $results[1];
        
        return array($real_threadid, $results[0]);
    } else {
        return false;
    }
}