/usr/include/GraphicsMagick/magick/ is in libgraphicsmagick1-dev 1.3.12-1.1build1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/GraphicsMagick/magick/analyze.h
/usr/include/GraphicsMagick/magick/api.h
/usr/include/GraphicsMagick/magick/attribute.h
/usr/include/GraphicsMagick/magick/average.h
/usr/include/GraphicsMagick/magick/blob.h
/usr/include/GraphicsMagick/magick/cdl.h
/usr/include/GraphicsMagick/magick/channel.h
/usr/include/GraphicsMagick/magick/color.h
/usr/include/GraphicsMagick/magick/color_lookup.h
/usr/include/GraphicsMagick/magick/colormap.h
/usr/include/GraphicsMagick/magick/colorspace.h
/usr/include/GraphicsMagick/magick/command.h
/usr/include/GraphicsMagick/magick/common.h
/usr/include/GraphicsMagick/magick/compare.h
/usr/include/GraphicsMagick/magick/composite.h
/usr/include/GraphicsMagick/magick/compress.h
/usr/include/GraphicsMagick/magick/confirm_access.h
/usr/include/GraphicsMagick/magick/constitute.h
/usr/include/GraphicsMagick/magick/decorate.h
/usr/include/GraphicsMagick/magick/delegate.h
/usr/include/GraphicsMagick/magick/deprecate.h
/usr/include/GraphicsMagick/magick/describe.h
/usr/include/GraphicsMagick/magick/draw.h
/usr/include/GraphicsMagick/magick/effect.h
/usr/include/GraphicsMagick/magick/enhance.h
/usr/include/GraphicsMagick/magick/error.h
/usr/include/GraphicsMagick/magick/forward.h
/usr/include/GraphicsMagick/magick/fx.h
/usr/include/GraphicsMagick/magick/gem.h
/usr/include/GraphicsMagick/magick/gradient.h
/usr/include/GraphicsMagick/magick/hclut.h
/usr/include/GraphicsMagick/magick/image.h
/usr/include/GraphicsMagick/magick/list.h
/usr/include/GraphicsMagick/magick/log.h
/usr/include/GraphicsMagick/magick/magic.h
/usr/include/GraphicsMagick/magick/magick.h
/usr/include/GraphicsMagick/magick/magick_config.h
/usr/include/GraphicsMagick/magick/magick_types.h
/usr/include/GraphicsMagick/magick/memory.h
/usr/include/GraphicsMagick/magick/module.h
/usr/include/GraphicsMagick/magick/monitor.h
/usr/include/GraphicsMagick/magick/montage.h
/usr/include/GraphicsMagick/magick/operator.h
/usr/include/GraphicsMagick/magick/paint.h
/usr/include/GraphicsMagick/magick/pixel_cache.h
/usr/include/GraphicsMagick/magick/pixel_iterator.h
/usr/include/GraphicsMagick/magick/plasma.h
/usr/include/GraphicsMagick/magick/profile.h
/usr/include/GraphicsMagick/magick/quantize.h
/usr/include/GraphicsMagick/magick/random.h
/usr/include/GraphicsMagick/magick/registry.h
/usr/include/GraphicsMagick/magick/render.h
/usr/include/GraphicsMagick/magick/resize.h
/usr/include/GraphicsMagick/magick/resource.h
/usr/include/GraphicsMagick/magick/shear.h
/usr/include/GraphicsMagick/magick/signature.h
/usr/include/GraphicsMagick/magick/statistics.h
/usr/include/GraphicsMagick/magick/symbols.h
/usr/include/GraphicsMagick/magick/texture.h
/usr/include/GraphicsMagick/magick/timer.h
/usr/include/GraphicsMagick/magick/transform.h
/usr/include/GraphicsMagick/magick/type.h
/usr/include/GraphicsMagick/magick/utility.h
/usr/include/GraphicsMagick/magick/version.h