I got 9/10. Chose the first one incorrectly.

For me, the giveaway for computer-generated images was that they don't focus on the "subject" and have too much detail on the background.

For example, look at the computer-generated boats - they blend into the background. It's hard to tell where the boat ends and the rocks begin, or where the sails end and the clouds begin. Or look at the grey house in front of the dude's face or the pipe behind the glasses lady's head, which bring in too much attention but add nothing to the painting.