An update: I have successfully made a *.djv document of 8 scanned images. Their total size was about 7MB of jpgs and the resulting *.djv file was 200 kB (with good quality)!
For those who would like to use it: If you have several images and want to bundle them in a document, you have to 1) open all of them one by one from the open menu, so they reside in their own windows. 2) Right click on the thumbnail of the second picture you want to add and choose "copy". 3) Go to the picture you want to have first and right click on its thumbnail and choose "paste after". continue that procedure until you have them all in the order you want.
There is also the option "insert page before/after" followed by an open dialogue. However, when I tried to add pictures that way the program crashed immediately and was impossible to open again. To be able to open the program again I had to delete the files in the temp directory that was produced during that process.
