var img;
function popimg(img_url)
{
    this.img = new Image();
    this.img.src = img_url;
    loading();
}
function loading()
{
    var h = img.height+40;
    var w = img.width+40;
    var str = 'width='+w+',height='+h+',resizable=yes,scrollbars=yes';
    if(h == 40 && w == 40)
    {
        setTimeout('loading()', 500);
    }
    else
    {
        window.open(img.src, 'popup', str);
    }
}