/usr/include/gamera/plugins/ is in python-gamera-dev 3.3.3-2ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/gamera/plugins/arithmetic.hpp
/usr/include/gamera/plugins/binarization.hpp
/usr/include/gamera/plugins/color.hpp
/usr/include/gamera/plugins/contour.hpp
/usr/include/gamera/plugins/convolution.hpp
/usr/include/gamera/plugins/corelation.hpp
/usr/include/gamera/plugins/deformations.hpp
/usr/include/gamera/plugins/draw.hpp
/usr/include/gamera/plugins/edgedetect.hpp
/usr/include/gamera/plugins/features.hpp
/usr/include/gamera/plugins/geometry.hpp
/usr/include/gamera/plugins/gui_support.hpp
/usr/include/gamera/plugins/image_conversion.hpp
/usr/include/gamera/plugins/image_utilities.hpp
/usr/include/gamera/plugins/listutilities.hpp
/usr/include/gamera/plugins/logical.hpp
/usr/include/gamera/plugins/misc_filters.hpp
/usr/include/gamera/plugins/misc_free_functions.hpp
/usr/include/gamera/plugins/morphology.hpp
/usr/include/gamera/plugins/neighbor.hpp
/usr/include/gamera/plugins/pagesegmentation.hpp
/usr/include/gamera/plugins/png_support.hpp
/usr/include/gamera/plugins/projections.hpp
/usr/include/gamera/plugins/runlength.hpp
/usr/include/gamera/plugins/segmentation.hpp
/usr/include/gamera/plugins/string_io.hpp
/usr/include/gamera/plugins/structural.hpp
/usr/include/gamera/plugins/thinning.hpp
/usr/include/gamera/plugins/threshold.hpp
/usr/include/gamera/plugins/tiff_support.hpp
/usr/include/gamera/plugins/transformation.hpp
/usr/include/gamera/plugins/utility.hpp