Even a mushroom expert can't identify an arbitrary mushroom from one photo. The reason is: either the photo reveals the surface features of the cap or the gill/

Even a mushroom expert can't identify an arbitrary mushroom from one photo. The reason is: either the photo reveals the surface features of the cap or the gill/hymenium features but not both. Same goes for the cap/stipe and any important underground features, like a volva (important for identifying many poisonous mushrooms). So...