I'm on Mountain Lion and installed ImageMagick using Homebrew (minimagick is also in my Gemfile but I don't think that's relevant). SimpleCaptcha uses it in a Rails app to create CAPTCHAs.
However, the image isn't created cause of this error:
Error while running convert: convert: unable to read font `/usr/local/share/ghostscript/fonts/n019003l.pfb' @ error/annotate.c/RenderFreetype/1123.
convert: Postscript delegate failed `/var/folders/gd/n7rzfhkd5jd0ws8jnzsz34hr0000gn/T/magick-vzHHz4ZP': No such file or directory @ error/ps.c/ReadPSImage/830.
convert: no images defined `/var/folders/gd/n7rzfhkd5jd0ws8jnzsz34hr0000gn/T/simple_captcha20121218-64930-1thtfpf.jpg' @ error/convert.c/ConvertImageCommand/3032.
Any ideas?
Looks like you're missing ghostscript. If you are using Homebrew you can install it via:
$ brew install ghostscript