After ios5.1, using a CIDetector and CIFaceFeature class can be easily face recognition.
refer a this tutorial: tutorial-easy-face-detection
if you want ios5.1 before check the this apple sample code: Square CAM
Body recognition, is you will need to use opencv library. Does not yet support by apple.
check out this pdf. this pdf also have a contents that how to opencv build for iphone. It will help you a lot.: face detection with openCV
If you are successful in face, body recognition by image. get a face and body bounds.
face and body image cropping and copy after Blur the entire image then paste it back into bounds, you seem to be.
