Some of these sites have images provided under a Creative Commons License, allowing various levels of free use of the content. Other sites fall under the Copyright Act. The Fair Dealing provision in the Copyright Act permits the use, in education, of an entire artistic work from a publicly available website (including a photograph, diagram, drawing, and chart), unless there is a clear notice prohibiting educational use. See the LRC's Copyright Guide for details, or contact the LRC. Make sure you always cite the images you use.
The LRC subscribes to a number of online journals and journal databases. When you search for a topic in the databases or in specific journals, you can use images that are associated with the resulting articles for educational purposes under the Fair Dealing provision of the Copyright Act. Don't forget to cite the images!