The easiest way to tell is a female's legs are all the same thickness. The male, on the second leg back from the front,has a much more massive "forearm" area. Think Popeye the Sailor Man. He uses these big legs to ensure a good tight grip on his lady friend when love comes sniffin around.
Overall, males tend to be slightly shorter and a bit less girth around the middle. The one in your picture...I'm leaning toward female, but give it a few weeks.