Okay.. I'll give you a similar hint to the one I had found:
All the paintings are featured in a rather famous book/movie. The solution key for the red chalk drawing has something to do with that book/movie and not the name or subject of that drawing.
I've been staring at that paged you linked since last night and tried every imaginable phrase except the correct one. I looked at it again after I saw your post and it finally dawned on me. Doh!!