title: Is it safe to ignore the possibility of SHA collisions in practice?
body: <p>Let's say we have a billion unique images, one megabyte each.
  We calculate the SHA-256 hash for the contents of each file.
  The possibility of collision depends on:</p>
  
  <ul>
  <li>the number of files</li>
  <li><strike>the size of the single file</strike></li>
  </ul>
  
  <p>How far can we go ignoring this possibility, assuming it is zero?</p>