Using images presents additional challenges because they often do not have any identifying information printed on them to help identify who owns the copyright of the item. Permission to use an image is most likely still needed, regardless of how difficult it is to find the owner. There are some sources to help find the copyright owner, or there are alternative sources of images that may be useful.
Using Images in Teaching
You may be able to use the images by relying on one of the statutory limitations within copyright law such as fair use or section 110 (1) which covers face to face teaching. If your use does not fall within one of these, you may need to obtain permission.
Using Images in Publications
This is actually the most frequently asked question at the library regarding copyright. If you want to use an image in a publication, you need to go through the same steps as using any other material. So, you first need to determine whether the material is still covered by copyright protections, whether your use is a fair use, or whether you need to obtain permission from the owner.
Finding A Copyright Owner
This is hard! If the image is not well known, it may be difficult to find the copyright owner. There are a few databases that may be of use though:
Google Image Search A Google search may reveal who the artist is, if you don't already know. If you use the advanced search features of an image search, you can filter by usage rights.
ARTStor A digital image library of over 1,000,000 images in the areas of art, architecture, the humanities, and social sciences.
Artist Rights Registry Once you determine who the artist is, you can check here to see if they are represented and licensing can be determined.
The Digital Image Rights Computator is a database that walks through a decision tree regarding the use of image. You need to know the copyright status of the image already though for best results.
Alternative Sources of Images
Kenneth Crews at Columbia University has compiled and excellent list of places to look for images that are in the public domain, or that have licenses attached that support noncommercial uses.