Videos, images and media files are protected by copyright in the same way as printed materials. Using images without permission for personal, educational or commercial use is against the law. Many collections are copyright-cleared for use in education but some may have restrictions so it is your responsibility to check the terms of use relating to any images you wish to use.
The University has some guidelines on copyright for University staff and students, see: http://www.ulster.ac.uk/copyright.html