The Millenium Bridge in London is a unique footbridge over the River Thames with a great view of St. Paul's Cathedral. Hundreds of people crossed this bridge during the long exposure. However, two men in the middle having a conversation stayed around long enough to show up in composition. The rest of the the people vanish due to the use of neutral density filters and a 311 second exposure.
To create a similar photo, you need a 10 stop ND filter, tripod, cable release and a lot of patience! My online course at BetterPhoto.com will be starting in November, (and it will be posted in October, thank you for your patience). We'll cover how to creatively capture long exposure imagery. I hope to see you there!