I know I mentioned before about freerice.com, a charitable website that gives you vocabulary questions and for every correct answer - they donate grains of rice.
However - they have added a new wrinkle that makes it even MORE of a time-sponge. New categories of questions! Including "Famous Paintings!" Can you identify the artists that painted these well-known paintings? Can you recognize their style well enough to id some of the more obscure ones?
To play, go to freerice.com, and to the upper right of the question, it says "Change Subjects." Click on this, and select "Famous Paintings" in the Art category. If you need a better view of the painting - just mouse over it, and it will enlarge, and shrink back when you move the mouse away. It is so cool. I've just wasted an hour already. Ok - not wasted - it's a learning experience.