Alice would like to detect, faces in a collection of sensitive surveillance images she own. Bob has a face detection algorithm that he is willing to let Alice use, for a fee, as long as she learns nothing about his detector. Alice is willing to use Bob's detector provided that ha will learn nothing about her images, not even the result of the face detection operation. Blind vision is about applying secure multi-party techniques to vision algorithms so that Bob will learn nothing about the images he operates on, not even the result of his own operation and Alice will learn nothing about the detector. The proliferation of surveillance cameras raises privacy concerns that can be addressed by secure multi-party techniques and their adaptation to vision algorithms.