I have a javascript application that I have written, and am trying to include a callback feature so I can see where the script is being used, I think I have it right in the javascript but am not sure what I should do on the other end to log the callbacks.

The code I have in the javascript is

var dcl=dc.location;
var dclh=dcl.href;
var f=document.createElement("IMG");
f.src="http://www.domain.com/,"+'?'+escape(encodeURIComponent(dclh)).replace(/\+/g,'%2B');

But what do I need to collect and store this information ?

Your server should be collecting the information in its request logs by default.
On apache (by default) its in /var/log/httpd/access_log
You could write a server app to create a more meaningful log by collecting more information about the user agent making the request.


I put together a similar thing a long time ago. You can see the code here:
http://willcode4beer.com/tips.jsp?set=jslogging