/* This uses the prototype.js library */
Event.observe(window, 'load', initOverlays);

function initOverlays() {
    for (var i = 0; i < document.images.length; i++) {
        var img = document.images[i];
        if (img.className == "zoom_overlay") {
            Event.observe (img, 'mouseover', addOverlay);
            Event.observe (img, 'mouseout', removeOverlay);
        }
    }
}

function addOverlay()
{
    var parts = this.src.split('.');
    if (parts[parts.length-2].substr(parts[parts.length-2].length-3, 3) != '_on') {
        parts[parts.length-2] += '_on';
    }
    this.src = parts.join('.');
}

function removeOverlay()
{
    var parts = this.src.split('.');
    if (parts[parts.length-2].substr(parts[parts.length-2].length-3, 3) == '_on') {
        parts[parts.length-2] = parts[parts.length-2].substr(0,parts[parts.length-2].length - 3);
    }
    this.src = parts.join('.');
}