Fiddler Crab is the common name for the semi-terrestrial crabs of the genus Uca. The males have an oversized claw or cheliped. If the large fiddle claw is lost, males will develop one on the opposite side after their next molt.
I recently stumbled upon a solution for determining handedness of a male fiddler crab from its photograph.
The procedure assumes that the photo shows front side of the crab and the fiddle claw is horizontal or nearly horizontal in the photo. The basic idea is to find out the fiddle claw and the hole formed between two pincers of the claw. From determining the center of mass of these two regions on the 2D image, it can be detected whether the crab is left-handed or right-handed.
The photo was shot last year during an expedition near the mangrove area of Reju Khal in Cox's Bazar.