That functionality where you click on a thumbnail image and it opens full size in a little window in your browser is called the lightbox. This morning I rewrote our lightbox tool.
The new re-write is MUCH better. It's much faster, looks better, and it greys out the background to make the photo stand out better.
Also, when you open the image full size, you can click on the image to close it. You can also click anywhere outside the image to close it. Lastly, you can hit the Escape key to close it.
If you find any problems with it, please let me know!