From the picture, you can see that the Rebel Flags do not look completely different from the US Flag when not fully extended in the breeze. In fact, if you were not told that these were Rebel Flags, you would probably assume that they were US Flags. This similarity in flags caused confusion in the war, and is what led to the
Confederacy adopting the "Southern Cross"
flag for use as a battle flag.
This is a fascinating image, showing the elite of the city in the House of Representatives viewing these prized trophies of War. This no doubt would have been an invitation only affair. The occasion appears to be a gala event, with the participants in their best clothes. Further research reveals that the event being celebrated was
George Washington's birthday. Harper's Weekly reported that events such as this one were held across the North to celebrate Washington's birthday.