Aaron (and Derek) were available as pregen player characters in a some of the modules, and these illustrations were used as the portraits on their PC cards in the back of the module. Eben's picture was likewise used for his NPC card.
In the days prior to scanners every drawing was photographed in order to add it to the layout. The percentages are the designer's instructions, to the photograph, for actual size the drawing would appear in the final document.
Larry Elmore was the very best for me for defining the look of the Dragonlance saga. I actually collected the older Boxsets adventures because of his cover artwork. And yes, I helped fund his Kickstarters. Though his latest art piece, The Women of Dragonlance was not top of his game.