Adding caption to gallery

Can you assist in displaying the caption over the large image in the gallery? I would like to have the “Photographed by XXX” appear at the bottom of the image. If I unhide the caption with something like this, then the caption appears on every image instead of just the image with the caption.

#top .avia-gallery .avia-gallery-caption {
background: red none repeat scroll 0 0;
bottom: 7px;
display: block;
position: absolute;
width: 100%;
}