Most of the images that can be found on the web will have some sort of copyright attached to them. If you want to use an image on the web, in a Power Point presentation or in WebLearn then you must first ascertain what the copyright allows you to do; this is necessary even if the image is used in WebLearn behind authentication.
The bottom line is that must always read the copyright terms and add attribution where it is required. I always add attribution even if it is not required as it seems like a nice thing to do – it also comes in useful if you need a different version of the image at a higher resolution.
I am indebted to Owen McKnight for pointing me towards Wikimedia Commons as a source of images and icons that can be used on web pages or in presentations, within the terms of their copyright licences. These licences are normally Creative Commons and make it easier for you to understand what you can do with the images. There’s also heaps of other media files such as sounds and videos.
Prior to this I have always used Flickr – using the advanced search facility and selecting images with Creative Commons licensing usually gives a large number of suitable images.
Damion Young from Medical Sciences has supplied an additional resource, Google: use the advanced search and in the Usage Rights drop down list select ‘Free to use, share or modify, even commercially’.
Dave Baker suggests ‘Creative Commons Search which is a meta search engine for CC items.