Well, photo's are usually nocturnal (though it depends on the subspecies) and very shy. I suggest setting up a camouflaged tent in an area where they're active and waiting for them to settle. If you find out where their den is you can just scoop 'em up in a fishnet
I'm sorry, I couldn't resist making a bad joke like that
It's mainly luck and patience. Luck with the right animals and positions (in my experience, smaller zoos have more interested animals), and patience with waiting for them to walk around and taking position.
Though you can also catch the attention of smaller animals with bright objects, I'm making a photo album with tiny, brighty coloured action figures and sometimes animals get really interested in them and go take a closer look (and after taking them away, they'll look right into the camera)
