Adding animal silhouettes to figures seems to be increasingly on trend in ecology. I have no empirical evidence to back up this claim, but it seems like every article in a high impact journal has at least one figure that incorporates silhouettes of species. I too am guilty of adding them – I find them a useful visual tool, but in the past, I’ve had to create them myself using photoshop. No more! PhyloPic (http://www.phylopic.org/about/) provides an easy to search collection reusable silhouette images of organisms from beetles to dinosaurs.
Resources like this are truly great!