var mainpic = document.getElementById('mainpic');
if (mainpic) {
        var imgs = document.getElementsByTagName('IMG');
        for(var i=0; i < imgs.length; i++){
                if (imgs[i] && imgs[i].className == 'thumb-small') {
                        imgs[i].onclick = function(){
                                var rel = this.getAttribute('rel');
                                if (rel &&
/\.(jpg|jpeg|gif|png|bmp)$/i.test(rel))
                                        mainpic.src = rel;
                                return false;
                        };
                }
        };
};