Drop tank. No fins.
Guys-- let's do some visual scaling. F-15/FA-18s are about 65 feet long, give or take an extremeity. Let's say the guy in the photo is 5.5 feet tall, and this thing is about 6 time his length. Or argue me down and say it's only 5 times his length. That would make this thing somewhere between 22 and 32 feet long. On a 65 foot aircraft?? Come on. Why would they need that large a fuel load anyway? Plus the 'rear' of this thing is 'squared'. Not at all good for airflow mgmt. Could this possibly be off of something really LARGE, like a BUFF, that needs to fly a long way, and perhaps this is only the front of it?
I am by no needs an expert, but we can all do a little more intensive photo interpretation before deciding this device is off a US fighter/attack aircraft.
This is my opinion, I welcome your flames ... 8-)