Augmented Reality for Jewelry Try-On

I want to detect the neck/shoulder area to augment the jewelry image on to it. I want to know the algorithm to do this and what is the easiest/simplest way using openframeworks to do this.

I know I can use face detection then use color detection to get neck/shoulder points and then draw the jewelry on to it.

But can you give me any detailed understanding for algorithm and using openframeworks.

Thank you.