libsixel.dll is libsixel 1.8.7 https://github.com/saitoha/libsixel/ DLL for Windows x86/x64, and built with option '-with-png=no --with-jpeg=no --with-libcurl=no --enable-python=no'.
libsixel provides encoder/decoder implementation for DEC SIXEL graphics, and some converter programs.
This software is provided "as is" without express or implied warranty.
See libsixel's License https://github.com/saitoha/libsixel/.