It comes down to how transformative the work is. They look at things like how much of the existing work you used and how much creative changes were made.
So grabbing your 9 favorite paintings and putting them in 3x3 grid is not going to give you fair use.
Cutting out sections of faces from different works and stitching them together into a franken face could give you enough for fair use if you made it different enough.
If only he had some way of reducing the amount of bombing.