I know the assignment is already over, but I have taken the picture outside the given dates, but it is one of my best pictures and I think it is a great example for DOF.
The picture shows an ice crystal on a frozen mountain lake (Hintersee near Berchtesgaden, Germany) close to where I live. It has been taken the day before Christmas 2007 on one of the rare occasions where the ice on the lake was crystal clear and there have been large and beautiful ice crystals all over the ice.
Camera was my Canon EOS 400D with a 28-300mm Tamron telezoom lens. The picture was taken at aperture 6.3 and 1/800 shutter speed with 300mm focal length (full zoom); ISO setting was 200.