Just because the image is copyrighted doesn't mean you are violating copyright law by displaying it. It would be quite nice of you to display a link to the site that Google found the image on - but if this is a non-commercial site, you have a very good fair use claim. If you really wanted to be in the clear, you could change your image search default to show "images labeled for reuse." Either way, don't be cowed by copyright maximalists.