There’s this great website called http://phylopic.org which is a collection of free silhouette images, either public domain or creative commons, depending on the person who submitted it.
Lots of people have been pitching in and we’re at over 2000 images now, but there’s still a whole lot more lifeforms left to do! Think of it as a giant pokédex for real life animals, and you’re helping people too! Anyone can pitch in, if you’ve got some spare animal photos that you have taken yourself, just trace over them as a vector or in a raster format and submit them!
These silhouettes are super useful for all sorts of things, but the main idea is to represent different lifeforms on a phylogenetic tree. Phylopic has some exciting features such as the ability to see the relationship between two organisms in a pictorial fashion.
I really suggest you check it out!