If you can't find a dependency using
# pkg search
You can always try using the web page:
http://www.freebsd.org/ports/
or
http://www.freshports.org/
Perl library packages/ports usually start with the name with
p5-.
In your specific case I would try installing
x11-toolkits/p5-Gnome2, that is just an educated guess from me.
I think most people here and the other board are going to use something simple like
graphics/scrot for a screenshot.