Note that BPG is based on HEVC still frames, and may be more patent-emcubered than current alternatives.
https://en.wikipedia.org/wiki/Better_Portable_Graphics#Paten...
https://en.wikipedia.org/wiki/Better_Portable_Graphics#Paten...
Currently the members seem to be working on converging VP10, Daala and Thor tech in the video realm but I'd guess images might be on their radar too.
And I dont know of any popular project that uses MPL apart from Mozilla Firefox.
Eigen (perhaps not "popular" unless you're interested in doing linear algebra with C++.. :-/ )?
Surely there are others as well..
If you want a weak copyleft license, IMHO MPL-2.0 is about the best available at the moment, and relatively easy to follow.