contour detection software

I need code for detecting and extracting an object from a picture. The input would be a JPG picture. The output, a PNG (or equivalent) with the "extracted object" in it and a transparent background. Intermediate output (optional) shall be a preview of the rough contour (e.g. red-line aorund object). Object countour shall be found by starting from a single point within the object and/or by a curve drawn around it. Code shall possibly be in Object-C for being integrated in an iOS app (iPhone and/or iPad).