/usr/lib/ruby/1.9.1/tkextlib/tkimg/ is in libtcltk-ruby1.9.1 1.9.3.484-2ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/ruby/1.9.1/tkextlib/tkimg/bmp.rb
/usr/lib/ruby/1.9.1/tkextlib/tkimg/gif.rb
/usr/lib/ruby/1.9.1/tkextlib/tkimg/ico.rb
/usr/lib/ruby/1.9.1/tkextlib/tkimg/jpeg.rb
/usr/lib/ruby/1.9.1/tkextlib/tkimg/pcx.rb
/usr/lib/ruby/1.9.1/tkextlib/tkimg/pixmap.rb
/usr/lib/ruby/1.9.1/tkextlib/tkimg/png.rb
/usr/lib/ruby/1.9.1/tkextlib/tkimg/ppm.rb
/usr/lib/ruby/1.9.1/tkextlib/tkimg/ps.rb
/usr/lib/ruby/1.9.1/tkextlib/tkimg/setup.rb
/usr/lib/ruby/1.9.1/tkextlib/tkimg/sgi.rb
/usr/lib/ruby/1.9.1/tkextlib/tkimg/sun.rb
/usr/lib/ruby/1.9.1/tkextlib/tkimg/tga.rb
/usr/lib/ruby/1.9.1/tkextlib/tkimg/tiff.rb
/usr/lib/ruby/1.9.1/tkextlib/tkimg/window.rb
/usr/lib/ruby/1.9.1/tkextlib/tkimg/xbm.rb
/usr/lib/ruby/1.9.1/tkextlib/tkimg/xpm.rb