Please enable the feature of switching to the next group by the left and right arrow keys when you reach the end of it. Don't force the user to use another key like up and down. Leave them enabled when you need to fast switch from one group to another, but when actively culling just don't make the user feel a blockage when he reaches the final image in a group. It would be much more fluent to just use the left and right keys to go through all images in all groups without stopping at the end of the group to use another key.
