Ok, we found the issue.
For some reason, the code that the control panel generates has this line
PiwikTracker::$url = "http://www.mydomain.com/piwik";
While in your “PiwikTracker.php” file, you have the $url defined as "URL"
So, if someone finds this same issue, by replacing the previous line with this one, it should work.
PiwikTracker::$URL = "http://www.mydomain.com/piwik";
… or at least, you won’t get the WHITE page.
Now, I am having some other issues.
When the code prints on my page, it is not decoding the URL; so my image link looks something like:
<img src="http://mydomain.com/piwik/index.php/piwik.php?idsite=1&rec=1&apiv=1&url=http%3A%2F%2Fmydomain.com%2Findex.php%3F%2Ftravel_info%2Fcameras%2Ftour2%2Finternal&urlref=http%3A%2F%2Fmydomain.com%2Findex.php%3F%2Ftravel_info%2Finternal&rand=515281839&XDEBUG_SESSION_START=&KEY=&cip=000.00.000.00&action_name=tour2" alt="" />
… Any ideas on how to address this?