How do I redraw or remove the picture of one chapter?

From version 1.9.22, on the book's page, in the Illustrations card, click the chapter's picture. You can write what the picture should show (or leave it empty and the AI chooses a moment), then press "Draw again". "Remove" takes the picture off that chapter. The chapter editor also shows the chapter's picture above the text. Editing or regenerating a chapter never loses its picture, because the picture belongs to the chapter, not to its text.