UFO Over New York Times Building? 2013

Witness States:

 I was in New York on a trip with a group of people I know. We had bought tickets for a double decker bus tour around the city on June 5th. It was evening time around 5:00-7:00.

We were on the bus tour, and we were taking pictures. I never went through the pictures until today June 30th, 2013.

I was looking through the pictures and saw a dark blimp like structure in the sky next to the New York Times building.

I never actually saw it at the time, but it showed up in my pictures, what do you think it could be?