Not just filler on the page.
It was back in junior high school that a quiz on a chapter in our history book asked us to explain something about a photograph on a page in the chapter. For most of us in the class a photograph on a page in a textbook basically meant that there was less text that we had to read. So rather predictably close to none of us in the class had devoted any effort to studying that photograph, and we complained that it was an unfair question. Our teacher then "explained" to us that he expected us to devote as much time to "reading" the photographs in the book as we did to reading the text. (For some of us, by the way, that may actually have been precisely what we'd done since we had little, or even no, intention of devoting much time to the text either.)
I doubt that I learned much of a lesson from that experience, though for many years I remembered what was in that particular photograph. I've also often wondered what it means to devote the same amount of time to "reading" a photograph as to reading a paragraph that takes up the same amount of space. They're clearly two different type of "reading" and I don't see how the time spent on them can be a measure of how well or intensely we've studied them.
Go to: How to read a Boidem column.