http: //www. gimp. org/screenshots/
The species of gallery where an individual click the thumbnail, as well as a bigger version loads without switching that page, or showing up in a fresh window
Lightbox is what you are searching for
http: //www. lokeshdhakar. com/projects/lightbox2/
yeah, as Jason mentioned, lightbox is what you need and I know to get a fact that the idea looks great, is simple to operate and best of most – solves your problem!
Ligthbox functions Javascript. For details, look at the particular page’s source, that ususally tells you a lot.