I would argue that if you really are abiding by free use, and you are giving a detailed reference for the work, that that creates a net positive for most creators because it brings attention to their work, and that increased profile enhances their hireability. It also increases traffic to the publisher's site. But I agree that it's a gray area. I try not to appeal to fair use unless I can't get a relevant image any other way. Most of the time, I just use http://www.publicdomainpictures.net . Lots of great free images on that site. But if you can't find a public domain image that is suitable, and fair use does not apply, then yes, you should just pay for an image or create one yourself.