/usr/bin/compare-im6 is in imagemagick 8:6.8.9.9-5+deb8u12.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/bin/../lib/x86_64-linux-gnu/ImageMagick-6.8.9/bin-Q16/compare
/usr/bin/../lib/x86_64-linux-gnu/ImageMagick-6.8.9/bin-Q16/compare