Well, the US Embassies at different countries have different ways of dealing with that "sending-back-your-passport" issue. In my country, the fee that I paid for the visa includes the payment for the courier that will deliver my passport. I really like this method because I can track my passport online and it is completely hassle-free.
I have to pay $900 for fees that are not covered by the assistantship, but it was clearly indicated that it will be deducted from my paycheck and distributed evenly every month.
If it was accepted through the online application, then you're good to go. But just to be sure, I suggest you bring another photo with you. I'm not sure if it's the same for all the US Embassies, but here in Manila, there's a photo booth in the waiting area/lobby.