When using images in a school project, it is important to cite your sources. It's best if you use images that are copyright free. If you find images using a Google images search, be sure to cite the image correctly (see the video below).
Photos for Class: This site will even add a citation as a caption for your image, which is a great way to include your image in a presentation.
Library of Congress: This is a great place to find historical images. Photographs found in this collection can be cited using the photograph entry on Easybib.