The answer to the question who's this, is Bessie.
Bessie is an American Bulldog who lives with us.
Here are some drawings of Bessie outside. In the lower picture Bessie is looking at a squirrel on the side of a tree.
Here's something else to look at. Bessie is a big dog. She's so large that her body doesn't quite fit in the box the artist drew. That box might also be called the frame of the picture.
Bessie is both inside and outside the frame of the picture.
You may also notice that the notebook the artist used is lying on a table along with some other tools for drawing.
We're guessing that the squirrel wishes he were somewhere else and not in the picture at all.