I have question about how to make a effective picture compression that can store multiple versions of a picture (with different resolutions), being compressed together (rather than separate).

Has anyone does something like this? Even if not, would you have an idea
how to do such a thing? The colours and shapes are going to be similar in
the different versions by the resolutions, so it seem to me that it could
be compressed to take advantage of that, somehow.

I think this might be helpful in TeXnicard, which I have already posted
about before (see <1587839656.bystand@zzo38computer.org> for details of
its compression algorithm). This would allow templates to include frames
and icons and other pictures at multiple resolutions, so that you can make cards printed at multiple resolutions, if that is needed.

In the case of TeXnicard, it would also be useful for it to encode CMYK + additional separations (if any).

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