In general, images copied from elsewhere that are reproduced in faculty/student papers or projects and which are available to only a limited classroom or conference audience, fall within the scope of fair use. Copies of images that are made available for the public at large, for commercial purposes (including publishing), or for an indefinite period of time usually require copyright clearance. Permissions or waivers from the copyright holder(s) and/or owners of the image(s) must be obtained. No matter what the circumstance, images copied from elsewhere need to be properly identified and cited.
The following links give examples of how to cite images from print and online sources.