Critical analysis of image and word is an essential discussion to have with children before, during, and after reading any well-illustrated and/or stimulating story. It is important for children to be active participants in understanding how pictures and story lines purposefully evoke emotions and convey meaning.
Early childhood educators often use picture books as a launch pad for art projects and dramatic play, so we are comfortable with looking "twice" at an image for the sake of those pursuits. Adding critical analysis to story discussions, especially regarding how images hold and express meaning (and yes, even to manipulate) will add rich layers to visual art pursuits while providing an opportunity to develop critical thinking skills and comprehension.
While I highly recommend Kolker as the resource, Molly Bang's Picture This is just the ticket to start a discussion with children and other adults. Line, color, and composition are all explored, compared, and analyzed. Children are absolutely capable of holding great insight and understanding -- their contributions to analytical discussions, once given the language and critical eye, are laser-like and deep.