Those guidelines are good. And I agree that an atrsit should use his/her own photos as reference whenever possible. But, as technology progresses so does the prospect of using photos in a multitude of different ways. For example…Using Google Streetview technology to do “virtual plein air” work. I’ve been playing with this for some time. Using a screenshot as a loose ref. With this application, you can virtually walk the streets, looking around with a 360 degree view.. Finding your comp is now up to you, and not the camera that recorded everything. It’s fun exploring. In fact, I’m 35 small studies into a U.S. state series, with plans to use the studies for larger works.I do think this technology can open some windows of opportunity for atrsits who are confined to their homes. It gives them a chance to see the world and pick their own compositions.Just a thought.