My menu is hard to read over a light photo. Can the photo be darker behind it?

Yes. In your site's CMS, open Menu Layouts, then Header menu, then Settings, and set Finish to Plain, with a darker top right corner over photos. The opening picture of each page then darkens gently toward its top right corner, where the menu sits, and stays clear everywhere else. Once a visitor scrolls, the header becomes the plain solid band. Default instead puts a dark gradient across the whole top of the photo, and Plain has no shade at all.