Suggestion 2: Checkmark next to the "good" Images, Label Each Individually

Since you have such a wonderful book that has already helped me, I'd like to give back with two suggestions for the next revision.  Here's the second:

It works well to have a circled "X" next to all the bad examples.   I suggest that you take this further and label each bad example individually, and also have a checkmark next to the good examples.  I've attached an illustration of this.

I hope that is useful.