I've been compiling my image library for the Birch Aquarium education department. It's been over a year since I last updated it. I've started with the easy groups of animals, like Birds, of which I only have a few drawings. I had to resize convert everything to jpeg form; some were photoshop, others illustrator, but jpeg is the easiest for teachers to handle.
It gets more complicated with say, Sharks, when there are: B&W outline drawings, Color images, Stippled images, B&W cartoon images, Color images, B&W stylized profiles, encompassing some 20 different sharks etc etc. Then I have to figure out an organization system that will make sense to a person searching for a shark image.