I am creating a presentation that includes some unmodified images licensed under either CC-BY, CC-BY-SA version 2.0, 3.0 or 4.0 (no CC-BY-SA 4.0) and some public domain images. They are all attributed. My original intent was to release the final presentation as CC-BY-SA-NC 4.0 as a PDF file, as my understanding/assumption was that,
- For some reason I assumed CC licenses to be forwards compatible
- I assumed that the work as a whole being CC-BY-NC-SA was ok, even if some images in it may have less restrictive licenses (which are mentioned) and given that these images could always easily be extracted from the pdf and then used under solely the original license.
Now I know that not all CC versions are forward compatible and I'm no longer sure if my second assumption was valid or if the presentation counts as a "derivative work", which cannot impose additional restrictions, and don't know what license I even could use if this is the case as BY and BY-SA would be incompatible in this interpretation.
Also CC BY-SA 4.0 is listed as incompatible with prior versions here. Does this mean I also could not release it under CC-BY-SA 4.0 if I wanted to and would instead need to remove all 4.0 images and release the whole document as CC-BY-SA 3.0 ?
I would appreciate if somebody could clear up my confusion about the licenses.