Cocoa (Objective C) Software modification

Hi everyone, I have an xcode project/source code (written in Cocoa/Objective C) that reads a barcode from the iSight camera on a macbook, then proceeds t decode the barcode in real time. I need to modify this software to read a barcode from an image and NOT the video stream of the iSight camera. In essence, this should remove a large chunk of the written code. For instance, I want to be able to take a picture of a barcode, input it into the program, and have it decode it to a number for me. All the decoding code is already there. I only need the ability to use an image as the input to be coded in. Feel free to ask any questions! Thanks, Brett