How to code Pattern Recognition?

I have an idea for a phone application that will require the user to use the phone's camera to accept an image and recognize words within the image.

An example of something similar is the QR Droid app. This app accepts images of QR codes and redirects you to whereever the code leads.

I want to do the same thing, but with words. What type of concepts are languages should I familiarize myself with to be able to do this?

Thanks!