The internet is a fascinating and wonderful source of images.
In this online environment it is easy to share and use what we find but it is important that we recognise that not everything we see is ours to use without acknowledgement or payment.
Whilst most would have no issue with someone, teacher or student, using an image in their work for educational purposes there are others who maintain their right to be paid for their work. It is both good manners and law abiding to consider the possibilities before downlaoding an image.
Rule three from Yahoo's '10 Best Rules of Netiquette states:
3. Respect Others' Copyrights: There are wonderful things online, information for everyone on just about any topic! However, these things have copyrights and licenses. Copying the works of someone else without permission or saying it is your own will not only ruin your online reputation, but could land you with hefty fines and lawsuits!
What can you do?
Most people use Google Images when they search for images. In the advanced settings you can require the search engine to return only copyright free images.
And, you can access images via the fantastic websites to be found on this page. NOTE not all of the images on all of these websites are copyright free you must read the information available to discern whether the image is appropriate for your needs.