It actually might be easier if you get a pic of the frog from the top. The cloaca of the female is very prominent if you look from above.
But you can only tell if the frog is mature.

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2.1 Ball pythons: Goblin, Nothing, and Bela
1.0 Boa Constrictor Imperator: Apache
0.1 albino Cranwell's horned frog: Bene
1.0 Tiger salamander: Slasher
1.0 black kittycat, Inky
A bunch of Oscar cichlids, one giant pleco, huge breeding lot of "fancy" (read: deformed) goldfish, and me an' the boyfriend.