When you shoot them from side to side like the two you posted pictures of, if you use a bullet that's fast or large enough, the shock disrupts the spinal chord even if it isn't directly hit. The only other shot that will also keep them on the bank when hit is to actually shoot the spine in two. Pretty darn good shooting, mec. Those old big frogs won't let you walk right up to them, either.
About recipes, I just roll'em in flour, salt and pepper and fry them. Not much is easier and not much is better!
Steve