Well I was trying to display a small logo image over another image (by default on all images) by using CSS but somehow nothing is displaying. Here is the CSS I used
img:after
{
    content: '';
    display: inline-block;
    position: absolute;
    width: 48px;
    height: 48px;
    top: 40px;
    left: 40px;
z-index: 1px;
    background: url(http://dl.dropbox.com/u/51558405/small.png) no-repeat;
}
The image on which I try to do this are standard 640x360 size. I thought using z index component for the background image might get it in front but no use. Since I wish to do this with all the images by default, I can't afford to use editing html manually so is there a way of doing this without having to edit html and just CSS or scripts?