US Copyright laws are complicated and hard to navigate and it isn't always clear when it is ok to use something even for educational purposes! This can present challenges for students when looking for images. I like to steer kids towards one of two options:
1) Take your own.
2) Use Public Domain and Creative Commons images! The New York Public Library just uploaded nearly 200,000 images and have made them free to use. This is great - if you happen to be looking for photographs of Ohio used cart lots in the 1930's. Another resource is a couple of clicks away when searching Google Images.