I get asked about this a lot.
As the library advice pages rightly say: It is a common misconception that there is an “exception” to copyright for educational purposes. In fact “fair dealing” only covers non-commercial research or study, criticism or review, or for the reporting of current events, but this does not extend to making copies of texts for students to use in the classroom, or to including images in presentations. It can be an infringement of copyright to include copyrighted images in teaching materials without permission.
Luckily there are a wealth of images collections which have been licensed for re-use with Creative Commons. In these collections you can easily see the permission you have been given and there is no need to undertake the onerous task of tracking down the copyright holder, or consulting a librarian.
Choosing Creative Commons images saves you time and effort as well as being good practice.
If you’re looking for content that you can freely and legally use, there is a giant pool of CC-licensed creativity available to you. There are hundreds of millions of works — from songs and videos to scientific and academic material — available to the public for free and legal use under the terms of our copyright licenses, with more being contributed every day. Flickr is a good place to start. Also Wellcome images, Wikimedia Commons, the British Library, Getty Images, Internet Archive or Edinburgh University Digital Image Collections.
Some of these collections even include handy tools to help you attribute the images once you have decided to use them so you will never again forget from where you got them.
JISC also provide a helpfulguide.