Mattias posted this exercise over at his blog.
Allow me to quickly translate/summarize: download the grid pdf on his blog (of much higher quality than the jpeg above). Print it out or open it in Photoshop or some other image-manipulating software. Draw the panel frames based on the straight lines in the grid (Mattias suggests using a lightbox if working over a print-out, but I think it might also be cool to draw directly on the print-out [EDIT: Mattias pointed out he does mention drawing directly on the print-out; I was just reading too quickly and like an idiot missed it. Sorry!]). Draw the images in the individual panels based on the elliptical lines in the grid. Et voila! (See Mattias' blog for illustrations of all the stages.)
If several people do this and send me the results, we could post them here all together.
I do think Mattias deserves to become a member of the blog for this, don't you? The invitation is on its way!