This is really a hard subject to get a handle on because things are still evolving and more importantly, is entirely based on opinions of the local court because there has not been enough precedence set on enough particular examples. .....
One of the most controversial is a painter who in his collage/painting used a number photographs stolen from a photographers site.
http://www.reuters.com/article/2013/...93O15E20130425 All he did was "transform" the other artists results. Figure that one out. Copy write lawyers insist this is outright theft but the court disagreed.