Fowler's have a slightly bolder, more leopard-looking pattern of spots, and normally inside each dark patch of skin they will have 3-6 warts, and the American will only have 1 or possibly 2 warts in the same area. You can see the 1-wart thing in the photo of that toad's back that you posted, so it's definitely an American, as others have already concluded.
Adult Fowler's:
http://www.outdooralabama.com/watcha...ig%20Guyer.jpg