I have installed Rmagick on my tiger with
http://wiki.rubyonrails.org/rails/pages/HowtoInstallRMagickOnOSXTiger/versions/new
I read that some folks have had difficulty, but it seems to work fine
for me. I was able to run a ruby example which uses it.

It is good to knwo there is a book on it, I will try to get it to see
what Rmagick does!