function highlight_image(doc, image_match) {
    var i;
    var image;
    var src;
    var name;
    var img_src_regexp = new RegExp(image_match);

    for (i = 0; i < doc.images.length; i++ ) {
        image = doc.images[i];

        name = image.name;
        src  = image.src;

        if (name.length > 0 && name.indexOf('menu') != -1) {
            if (src.match(img_src_regexp)) {
                src = src.replace(/_off\./, '_on\.');
            }
            else {
                src = src.replace(/_on\./, '_off\.');
            }
            image.src = src;
            // alert('image: ' + src);
        }
    }
}