Changes to cart module

I'm an experienced developer, but new to PHP and I think some of my hangups may be coming from there...

We need to have the ability to add resizes/derivatives to the cart instead of just the full-sized image. I have been sifting through the code and trying to work out what I can, but it's been a painful process for me. I understand there are a lot of API calls to document, but what currently exists is really not all that useful for me.

I sort of follow how the imageViews array of the them is used to display the proper image when chosen from the select list. And I've finally found some examples of how to get some of the derivative information from the APIs. Is there an example of how I can tie this information together somehow or could someone possibly give me some pointers?

Thanks for any help.