Checkout type module with background processing

Hello everyone,

I want to write my own module that will allow me to launch a background process on my server to process the selected images (essentially put presentation frames on the images), zip them up, and then email them out.

I figured the best way to start is to use a checkout module but I'm not sure which of the many checkout modules would be the best one to start with. Ideally, it would be one that has some straightforward code so I can better understand how the Gallery API and templates are working.

Suggestions?

Thanks

-alex