The dialogue (when there is dialogue) is on the card under the image. In the first image, you'll see a lot of cards without dialogue.
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What I thought was interesting, as well, was that in this pitch portion of development, they aren't very concerned with how high the quality of the images is. That is, it's easily something most of us could doodle with a bit of practice.
Terry Rossio talks about pitching using storyboards, so I don't see why any screenwriter shouldn't get a book on basic cartooning, and learn to storyboard their own work, whatever genre the screenplay is.