I've had a few pics published in books and magazines, although the income it generates isn't a drop in the bucket (this year I was able to buy a new macro lens with the "take", but generally it is just a trivial amount).
As Scott said, get your stuff out there. Once people see/know you take good shots, they may come looking for you.
You can also submit images to magazines or book publishers, but realize the competition is fierce so your shots have to be as good as or better than those already in the best books and magazines. Your pictures must be perfect because the people that evaluate them are experts at picking out problems in photos.
You can also write an article for a magazine and include your pictures since you get paid for the article and the pictures. Every year or so the hunting/fishing magazines publish an article on snakes and I am usually surprised at the poor quality of the photography. You could certainly try submitting to someplace like that.
I have also been approached by people looking for pictures on several occasions. One thing that has been consistently true is that people have needed pictures of either very uncommon species or very common species.
Here are some examples to show you what I mean -
- I was approached by Carl Ernst when he was putting together his Snakes of North America book. Why? I had the only known (?) photo of a snake that was IDed as Tantilla atriceps from the US. The rarity of the photo made it "valuable" (I got a free book out of it).
- Texas Parks and Wildlife Department approached the University I was affiliated with to try and put together a poster of common Texas snakes for distribution to schools. Several people in the area that had good herp shots got together and found that while we had some incredible shots of uncommon animals, we didn't have great shots of the really common stuff (Texas Ratsnakes, for example). It was an eye opening experience. Ask yourself - Do I have good photos of the 10 most common herps around here? If not, it could be a good project.
- I have been approached by local groups, like Audubon societies to provide slide presentations on local snakes.
- Dick Bartlett is writing a book about Sandboas and their relatives for Barrons Press. He had seen my website and contacted me about photos of some less common species. So the combination of having pics of uncommon snakes and having on the web sold some pics for me.
So, my point is the pictures that sell will be excellent shots of common species that people often overlook, rare species that people don't have good pics of, and shots with a new perspective or that tell a story.
You aren't going to sell many pictures of albino ball pythons because those photos are a dime a dozen.
-----
Chris Harrison