Five Types of Information You Must Acknowledge
5: You must acknowledge Graphics, Photos and Other Visual Material
It's so easy to cut and paste images from the web and make photocopies from books that students sometime forget these materials belong to someone else, just like written words. You need to acknowledge these sources.
Occasionally a web site will specify "permission free" or "no permission required." It's still a good idea to cite the source just so your reader knows where it came from.
Sometimes a web site will show you how to cite the source if you just dig around a little. The image and citation below are an example of such a site.