function highlight(offset){
    var thumb = document.getElementById("thumb_" + offset);
    var input = document.getElementById("image_" + offset);
    if (!thumb || !input) {
        return;
    }
    if (input.value == 1) {
        input.value = 0;
        thumb.style.border = '';
        thumb.style.margin = '2px';
    } else {
        input.value = 1;
        thumb.style.border = '2px solid red';
        thumb.style.margin = '0px';
    }   
}