Well, these are public images, offered to anybody who wants them. I cannot see how any (commercial) harm is inflicted to Jolla by caching them unaltered.
Also, is it possible to get at the images without logging in first, …
Yes, there is only one kind of images, the (public) “trial” ones are identical to the ones offered when one is logged in.
… with “No”, but not naming a reason.
Come on, we all know that Jolla wants us to beta-test their products, originally SFOS, nowadays primarily AlienDalvik. They repeatedly stated that they will never offer older SFOS versions for download, because we all should always be using the most recent one. If one does not, one evaded the typical SFOS-user role as a beta-tester, which detrimental for Jolla’s product development.
Hence I would not ask, just do. If Jolla really sees a legal issue, they can always name it. But without having a specific issue pinpointed by them, one is free to assume there is none.