title: tracking pixel or javascript include?
body: <p>I am building a tracking system for refererrals to our websites and on behalf of other 3rd party website owners.  This will include placing a cookie when a customer clicks through to the site and subseqently reading their ID from this cookie if they reach the defined 'success' page.</p>
  
  <p>I have seen a number of different methods used for tracking and they all seem to fall into 2 categories:</p>
  
  <ol>
  <li><p>Including an IMG tag which will link to a script that processes what it needs to and returns an image</p></li>
  <li><p>Including an external javascript file, usually with the same approach as in 1 within  tags.</p></li>
  </ol>
  
  <p>What are the benefits of one approach over the other?  I feel I must be missing something quite simple here however can only see that the javascript approach can be used to avoid image caching.  </p>
  
  <p>The server-side script is ASP.net</p>
  
  <p>EDIT:  The cookie / tracking approach is being used because it seems to be the industry standard, and we need to be able to track goals over a long period of time and / or many visits however alternatvies to this approach would be welcomed!</p>
  
  <p>Thanks</p>