The pillow-heif wheels bundle several libraries that are compatible licensed. Here they are listed.

Name: libheif
License: LGPLv3
Files: heif.dll or libheif.[dylib|so]
  For details, see https://github.com/strukturag/libheif/blob/64d9ab99ce7ea8876700c034b19bbc8dd773ae0b/COPYING
  Source code: https://github.com/strukturag/libheif/blob/64d9ab99ce7ea8876700c034b19bbc8dd773ae0b

Name: libde265
License: LGPLv3
Files: libde265.[dylib|so|dll]
  For details, see https://github.com/strukturag/libde265/blob/e587ef6e8000662b91c35ccb866c2374d3a40e27/COPYING
  Source code: https://github.com/strukturag/libde265/blob/e587ef6e8000662b91c35ccb866c2374d3a40e27

Name: x265
License: GPLv2
Files: libx265.[dylib|pyd|so]
  For details, see https://bitbucket.org/multicoreware/x265_git/src/Release_3.4/COPYING
  Source code: https://bitbucket.org/multicoreware/x265_git/src/Release_3.4

Name: libaom
License: BSD 3-Clause
Files: aom.dll or libaom.[dylib|so]
  For details, see https://aomedia.googlesource.com/aom/+/refs/tags/v3.3.0/LICENSE
  Source code: https://aomedia.googlesource.com/aom/+/refs/tags/v3.3.0
