title: Is it possible the MD5 of two different strings be identical?
body: <p>I'm trying to create a dynamic avatar for my website's users. Something like stackoverflow. I have a PHP script which generates an image based on a string:</p>
  
  <pre><code>path/to/avatar.php?hash=string
  </code></pre>
  
  <p>I want to use the MD5 of users' emails as the name of their avatars: <em>(and as that string PHP script generates an image based on)</em></p>
  
  <pre><code>$email = $_GET['email'];
  $hash  = md5($email);
  copy("path/to/avatar.php?hash=$hash","path/img/$hash.jpg");
  </code></pre>
  
  <p>Now I want to be sure, can I use the MD5 of their emails as their avatar's name? I mean isn't there two different strings which have identical MD5's output? In other word I want to know whether will be the output of two different strings unique?</p>
  
  <p>I don't know my question is clear or not .. All I want to know, is there any possibility of being duplicate the MD5 of two different emails?</p>