I don't envy this task. Image recognition isn't a trivial task. When i was in college I did some work with Neural Networks. The trick was to represent the data in some numeric/data means and then train the neural net by showing it a whole lot of solutions to the problem. The work you've done to create/enhance edges is definitely a step in th right direction. Then using a Neural Net, you'd have hundreds of valid images and images that were "rejects" and "Valid" and eventually you could train the neural net to pick the right images. There's a whole science behind how to setup such a network, and what is right for which situations.

I doubt there's an API or module that simply does what you want, that's anything other than experimental, but it's been ages since I've looked at the technology. There are sw tools for image recognition based upon Neural networks, and doing a quick google search for Perl Neural Networks yields a few links (looks like there's even a perl module). That might be one direction to investigate, but you've probably got a lot of experimentation yet to do. Good luck.