Hello, adebeo gives you an address to find some resources for your images, a bank of 2D images already clipped: http://www.lespaysagistes.com/ressources-gratuites/banque-image/banque-images.php
In this image bank you will find trees, skies, vehicles as well as characters. The images can be downloaded in PSD format. All these images are free of rights, so you can use them as you wish.