title: How to use SIFT algorithm to compute how similar two images are?
body: <p>I have used the <a href="http://en.wikipedia.org/wiki/Scale-invariant_feature_transform" rel="noreferrer"><strong>SIFT</strong></a> implementation of <a href="http://www.vlfeat.org/overview/sift.html" rel="noreferrer"><strong>Andrea Vedaldi</strong></a>, to calculate the sift descriptors of two similar images (the second image is actually a zoomed in picture of the same object from a different angle).</p>
  
  <p>Now I am not able to figure out <strong>how to compare the descriptors to tell how similar the images are</strong>?</p>
  
  <p>I know that this question is not answerable unless you have actually played with these sort of things before, but I thought that <strong>somebody who has done this before might know this</strong>, so I posted the question.</p>
  
  <p>the little I did to generate the descriptors:</p>
  
  <pre><code>&gt;&gt; i=imread('p1.jpg');
  &gt;&gt; j=imread('p2.jpg');
  &gt;&gt; i=rgb2gray(i);
  &gt;&gt; j=rgb2gray(j);
  &gt;&gt; [a, b]=sift(i);  % a has the frames and b has the descriptors
  &gt;&gt; [c, d]=sift(j);
  </code></pre>