With puzzles, we expect to find concealed instructions for how to solve the puzzle, as well as confirmation within the puzzle along the way. Without those two things, we're just blindly guessing.
Let's analyze Painting 1 with that in mind:
Choosing instructions is just playing out a series of assumptions and seeing what shakes out. Here are a couple of assumptions that we can make (nothing new)
The backwards G and h at the top of the dress tells us that we need to look at the mirror image of the painting
The upside down Roman Numerals in the middle of the dress tell us that we need to rotate the painting
In 1982, you'd turn the book upside down and hold it up against a mirror. Today, I can show you what it would look like using Photoshop.
With these assumptions, the Roman Numerals that were previously upside down and reversed, are now right side up. On the left side we have a clear V, the Roman Numeral for 5. On the right side we have a clear IV or Roman Numeral 4.
The painting is giving us a 5 and 4.
The next thing that jumped out at me was the pointing fingers. The pointing is such a central piece of the painting, that we have to assume it's important to solving the puzzle. We always hear about the fingers pointing to the blue blocks, but if you look closely enough, the fingers are pointing to the lines between the blocks.
With the painting still in it's mirror and upside down state, we can count the lines between the blocks from bottom to top. On the left side, she is pointing at the 5th line, on the right, she is pointing to the 4th line.
On the left side, a Roman Numeral for 5 and a finger pointing to the 5th line.
On the right side, a Roman Numeral for 4 and a finger pointing to the 4th line.
That can't be a coincidence.
I believe that the Roman Numerals (V and IV) are confirming that the pointing fingers are, in fact, telling us 5 and 4.