Regarding cross-platform image support for clipboard sharing, just figured out that SDL2 itself only seems to support text.
However, a little research brought those websites, which might help:
https://github.com/dacap/clip
https://playcontrol.net/ewing/jibber...Prototype.html
https://jtanx.github.io/2016/08/19/a...board-library/
https://forums.libsdl.org/viewtopic.php?p=24823