I enlarged the photo to get a better look and still can't tell. The anal glands are inside maybe a quarter to a half an inch. There are two of them, one at 4 o'clock and one at 8 o'clock. I think if it were that there might be an odor. Couldn't tell if you had opened his anus a little to take the picture or if the spot is on the outside. I agree that I would take him to the vet. Good luck and keep us posted.