I am no pro with scribus, but I know that images can be linked or embedded. The first method requires that the .sla file and all the image files stay put in their folders and the relative position of these folders is not changed. The links must be preserved.
With embedding, the images is written into the .sla file
pros and cons
Embedding is good for small projects with a few images. You have the flexibility that is inherent in a stand alone file. copy it, move it, etc.. and all is still contained in the .sla, though it could be a bit of a larger file
Linking on the other hand suites larger projects. the .sla file does not get bloated with all the images and remains nimble to work with.
If your images do not show, could be because the links are broken.