If you look in the file listing for http://api.metacpan.org/source/KENTNL/MetaPOD-0.1.3/examples/ , you'll see it clearly knows the MIME type of the images in that dir:
Name Size Type Last Modified
Parent Directory
self_structure.dot 725 application/msword Sun, 02 Jun 2013 08:28:08 GMT
self_structure.pl 859 text/x-script.perl Sun, 02 Jun 2013 08:28:08 GMT
self_structure.png 27951 image/png Sun, 02 Jun 2013 08:28:08 GMT
However, if you view the png file
http://api.metacpan.org/source/KENTNL/MetaPOD-0.1.3/examples/self_structure.png
It gets dispatched as text/plain
Which is not very useful.