An image of a set of scales. On the right side, there is a small version of Granger standing, being weighed. The left side of the scales is filled with small versions of other characters: Voldemort, Dumbledore, McGonagall, the Dursleys, Zabini, Crabbe, and Goyle. A hand reaches from above and pushes down Granger's side, so it appears that Granger is weighed heavier than all the others put together.
At the bottom is the chapter title:
The Harshest Judge
This will be a chapter about Granger!
The illustration was inspired by the Ancient Egyptian myth that, in the afterlife, your heart/soul is weighed against a feather. If it's heavier (meaning more evil) than the feather, then it will be devoured by a monster.
Incidentally, I've known what this image will be for a long time. For the earlier chapters, I've invented most of the title-page visual metaphors on the same days I drew them, but for this one and the next one, I've known since before I drew the first page.