[solved] CAPTCHA gem: undefined method `stringFT'

Since it took me quite some time to resolve this problem, I hope this
post will be useful for someone else.

I am using the CAPTCHA gem in my application and always got the
following error:

undefined method `stringFT' for GD::Image:Class

It turns out that I was missing the GD libs for ruby. I'm on ubuntu, so
a quick
sudo install libgd-ruby
solved the problem for me.

I also found resources for OS X and Red Hat Enterprise Linux 4:

OS X: http://lukewarmtapioca.com/2007/02/06/gd-on-osx-and-ruby-stringft/
Red Hat: