As a volunteer and a co-founder of an animal rescue team, I've done a lot of photography of cats and dogs that were in shelters we ran. Some of these photos were later put to good use in finding suitable permanent homes for our sheltered animals, and the initial impression would-be adopters get from such photography makes for a huge difference. Sometimes, I was also asked to prepare other promotional materials, such as posters or website graphics, using photos I took.
As this photography work takes a lot of time and patience, both shooting as well as later editing for various promotional materials, having a dedicated photographer-volunteer would mean a world to us, both other volunteers going about all kinds of time-consuming chores, as well as the animals in need of a new home. It really made a huge difference, and we had positive response from all over the world, later successfully finding homes for hundreds of stray cats and dogs from Romania (I was working there as an expat) throughout Europe.
Just a collage of a few photos that made a difference. Obviously, I'm not a professional photographer, but I do try my best.
If you love animals and have the patience to wait endlessly for that perfect photo moment while in the company of other think-alike volunteers, then I think your efforts would be greatly appreciated in such teams and/or organisations. But there's also a need for less than perfect photography. Some sheltered animals would already have found a suitable new home, but were awaiting transportation. In the mean time, of course, adopters need to be updated on the status of their new pet. The list of how you could be useful is really endless. Of course, you could benefit to such charitable societies a lot more, if you could combine your photography skills with some other as well, say organizational skills - e.g. organizing photographic exhibitions, protest (organized, with good intentions) even, or - God forbid - even guerilla photography of discovered animal abuse that needs to be documented and reported on. But even without other skills, if you didn't live half way around the world away from Europe, I'd be asking you for your details by now, begging you to join us. ;)