And just a helpful site to help you track an image... see TinEye. It can show you all the places a particular image is used on the web. I've used it successfully to trace an image back to the copyright holder so I could ask for usage rights.
Can anyone tell me the laws concerning using images from Google images in my work? Are they copyright ?
British Museum: Coin with head of Alexander the Great. If you click on the image, it gives you link to investigate the terms and conditions for digital images.