title: What is the method to detect whether a given picture is human face or not?
body: <p>Is there any simple algorithm to judge whether a given image is face or something else (without training hopefully)? </p>
  
  <p>My thought is to construct the eigenvectors of each image, then apply some clustering method (for example k-means with k = 2). But I'm not sure what will be the best criteria to distinguish face/non-face even if a good clustering result is obtained?</p>