Ask HN: What are the legal areas of patent use in software development?

I know the title was a bit vague but effectively a buddy and myself are starting to think about developing some mobile apps based on the research I did during grad school.

Using techniques like face detection and feature extraction (for example Viola-Jones), are there things I need to know from a legal perspective about using them in my software?

Also, I'm planning on sitting down with my former professors to discuss implementing their patent (I think it is still pending but they obviously have a lot to do with my learning).

I want to make sure if I'm doing X,Y, and Z, Y doesn't get me in trouble. If HN can steer me into the right areas or required reading, I'd greatly appreciate it!