An interesting topic.

I am one of those people that use images from say DA and sites like it. I don't change up the image or anything like that nor do I take ownership for it. If anything, I use it as a reference. What I mean is that I would write up a basic description for a character like "tall, slender, white hair, red eyes". If by chance that I come across an image that fits my descrption, then I'll use it as a visual reference.  I don't think I'm doing anything wrong since I'm obviously not making any profit off of it. If anything, I think artists should be flattered that so many people use their images. It just means that they're doing great work. The fact that people use their images as visual references is proof of that.