If you install the Linux photobook software - or just download it and read the EULA, you find this:
4.6 Authorized cewe-photo-provider and its suppliers claim no ownership of Your personal photos. You hereby grant us a non-exclusive, royalty-free, fully-paid perpetual licence to use, download, upload, copy, print, display, reproduce, post, transmit and distribute these photos in the normal course of our business.
Then if you look at the example photobooks linked from the regular photobook page you posted, you'll quickly see that those are all real books made by customers of CeWe. Which implies what the normal course of their business is.
I don't like that, and I'll have my future photobooks printed elsewhere.
As I mentioned, plenty of photo houses are willing to print books based on jpgs. I asked 3 and got the positive response from 2.


Which fotoinsight designer software / software to make photobooks with are you referring to, that runs on Linux?
I couldn't find any other than the CeWe version.