Won't be able to tell from the pic. Find out the size of the nut on the pinion. Can't remember 100% the sizes but the 50 uses a smaller nut than a 60. I think they are 1 1/8" (50)
1 5/16" (60) or metric equivalent. I think.
The lip or ledge in the top of the casting on the backside of the cover is more pronounce on a 50. Hard to describe but once you see two side by you can tell.
judging by the length of the pinion snout, and the lip on the housing, I'm gonna say it's a 60.
From the front, the axles look the same (using the same size diff cover and all), but from the pinion side, it's pretty easy to tell it's a 50 just by looking at it. They almost look like a smaller diff snout has been cast into the "hoop" of a D60.