Click on any image to see a full size version.  The picture will open in a new window.  If you don't close the new window, and switch back to this page of thumbnails, the next thumbnail you click will open in that same new window.  But this time it will probably remain behind the thumbnails and it will seem like the new picture didn't open until you manually switch windows.  If you don't want to close the new window each time, the alt-tab key combination will alternate between the thumbnails and the most recent picture.