Photo pin is easy to use. It has a search box where you can type in your topic and preview the image before you can finally download it. The thing about photos downloaded in Photo pin is that they always have a credit link back to the photo owner.
"PhotoPin uses the Flickr API and searches creative commons photos to use for your blog. (Note: we are not associated with Flickr in any way, other than powering our search results using their API.)"
