Is my cat male or female

We were told she is female but I'm starting to think she's male? 

She has a distinctly male look on this photo!  We usually refuse to sex animals absolutely online, but for anyone reading, here is how to sex a cat:  have them facing away from you with the tail straight up.  Find the rectum where the poo comes out, the round hole that has muscular 'elastic' around it to keep it closed, the higher of the two, closest to the tail.  The rectum is the same in most cats. Below this is a second hole.  It is either a round hole about an inch (or two or more finger-widths) below the anus, possibly with a pair of testicles (either developed in the sac like so, or the saggy vestigial suggestion of where they might appear) between the two.  In this case, the cat is male and the second round hole is the very end of the penis, which points backwards in cats.    Or else the lower hole is actually a small slit, which starts soon after the anus finishes (not quite touching).  This would be a vulva.  There are many pictures online which will help to illustrate what I'm saying.  Your vet will always confirm.  Best of luck!

(PS I have obviously not examined this cat, but it looks to be a male with a large pair of testes on this photo!)

To summarize: If there are testicles, this is a male.  The cat in the picture looks to be male and I would be surprised if it wasn't, although one cannot sex from pictures and ought to confirm with a vet. If there are no testicles, look at the distance between the anus (muscular hole at the top where the poo comes out) and the hole below it.  In males, the lower hole (the end of the penis) is usually round and usually getting on for an inch clear of the rectum (depending on the size of the cat).  In females, the lower hole is in fact a slit, and is closer to the rectum.

He looks like a male cat.