"Use any of the Work as part of a trademark, design-mark, trade-name, business name, service mark, or logo"
That may not include book covers, but considering the fact that the title will be laid over the image, I'm not sure. This also means I'd be manipulating the image, and that's often against TOS.
As a side note, some sites also seem to restrict the use of any of their images for anything sexual, so that could be bad news for anyone who needs images for their erotica ebooks.
Does anyone know of good affordable image sites that don't have these types of restrictions? I guess that as a last resort, I could contact the creators of the images directly and ask them exactly what they're okay with.