IMPORTANT – Internet images are not by default public property! Most images on the internet may not be reused in posts without permission. The unauthorized use of images may result in a rather forceful demand to remove them immediately, or the threat of legal action.
As a result, sourcing images can be tricky. However, there are a number of good resources for finding images that are useable (see below). In addition, here’s an excellent article by PF Anderson on image sourcing and use.
Remember: Image sources should be acknowledged – more information on this here.
Note: One thing to look for is images that are posted under a Creative Commons license – within the limitations of the specific license agreement, these images are generally useable.
Sources of free images. Important: please ensure all images are appropriately acknowledge in posts.
Free images – check the conditions of use though
Collection of Creative Commons images