Yes and No, car dealerships put cars they would never get on their site, to add some eye candy. there is nothing wrong about it.
For the most part pictures on the net are fine to use on your site along as they are not copy written.
always remember you are a small fish and nobody will go after you for infringement, however always keep this in the back of your head. look what happened to YouTube, Google, FaceBook, they all started small and grown into multi billion companies. if there was a picture on the site that was from someone else then I would expect a law suite because it would be worth it now.
so to protect you I would go to your local zoo or reptile store and ask them if you can take some pictures of there animals to put on your site, tell them you will put a link to there store/zoo for credits.