This could have ended in several ways. A - you spotted all the differences like a normal person. B - you got too freaked out by the Mona Lisa stare and couldn't concentrate, thus failing the task. C - you booked flights to Paris to meet her in real life. Okay, the flight to Paris is kind of outrageous, but we've been thinking about it a lot these days.
The first difference might be one of the easiest ones on this whole list. In the first image there is no ring on the Mona Lisa's right hand. In the second image, it's very much there, and she even looks kind of smug about it, somehow. The second difference is a little subtler, but it can be found right by Mona Lisa's right elbow. A ledge present in the first picture has been completely removed in the second one.