I was watching a show last night on Edison and his inventions. One of the early lessons he learned, was never build anything that won't sell. Your pure Perl version of this cropping app, will be so slow, that nobody will use it, since most people can install and use ImageMagick, GD, or Imager ( or it is preinstalled for them). If this was used in online web apps, the first thing that would happen, is you would get alot of cgi carshes due to timeouts( as your Perl script uses 12 seconds to do what the c-based module does in .3 seconds).

It will take alot more effort to make your app(bug free), than it would to learn how to install and use the existing modules. It reminds me of myself, when I was a purely functional programmer, and would spend hours trying to avoid using objects, because I didn't want to learn how they worked.