These videos show some approaches to that kind of result:
Start here to learn After Effects: http://adobe.ly/bjBT3P
Using Todd's fantastic Motion Tracking and Rotoscoping tutorial all you have to do is apply a levels or curves effect to the white solid to brighten up and highlight the part of the shot you've masked off:
Put a black solid solid on top of your footage, set it to multiply and reduce opacity. On top create your shape e.g. as a masked layer, assign it as the matte for the solid and use keyframes or motion tracking to mocve the matte shape around and have it follow your object.