Some people can make a guess judging by the length of the tail, and possible hemipene bulges just after the vent. That isn't always accurate. Probing has never failed with my corns. A vet visit is costly, but try to find snake breeders in your area, if possible, who may probe the corn for you. Look up herp societies in your area too. Sometimes local rescues have a vet who visits to check on their new rescues. You may be able to make a deal to have your corn checked by making a contribution to the rescue. ( my camera doesn't take good pictures either, and there's no way my wife will hold a corn still enough. One squirm and the corn gets put down on the carpet)