You could look at the Moultrie M-80 Black Flash trail camera,it suppose to have a flash at night that is un- detectable then set it to take the streaming video during the day time and pictures at night!Go to www.chasingame.com to read the reviews on it.If You can set the camera up at the sight they dump the trash maybe You could get a decent license plate picture if they are slowing down?

Another Camera to consider is the Uway UM-562 I believe....it takes a picture and sends it to Your cell phone, that might help You catch them also?