Most image suppliers indicate how their images can be used. For example, compare the very different licenses from these vendors:
"AccessMedicine users may display, download, or print out images associated with the site for personal and educational use only. Educational use refers to classroom teaching, lectures, presentations, rounds, and other instructional activities, such as displaying, linking to, downloading, printing and making and distributing multiple copies of said isolated materials in both print and electronic format. Users will only display, distribute, or otherwise make such images from the applicable AccessMedicine site(s) available to students or other persons attending in-person presentations, lectures, rounds or other similar instructional activities presented or given by User..."
The Digital Anatomist Project "The interactive atlas software is free for non-commercial use, as long as this copyright remains... We hope and expect that others will use the package to develop their own Web-based atlases, and will provide us the links so that we may include them on the Interactive Atlas directory page."