Well this picks up on radio transmissions on 137Mhz. Webcams would need to be transmitting, and most people don't have wireless webcams. Street cameras do transmit (like the ones you see when the news shows traffic congestion), but they usually use point-to-point microwave links to traverse the distance.
There are ways to pick up the cameras that operate on 800, 900, 1200, and 2400 Mhz. Like the room monitors, or baby monitors, that people might have. Typically this is as simple as putting a larger antenna on a receiver. (Since most scanners won't go into the ranges required).
If you wanted to pick up these cameras, the best thing to do is buy some simple receivers on ebay (since the cameras aren't protocol specific usually), modify them to be battery powered (simple, because they don't use much power just to receive), get a large antenna (probably a yagi with a high gain), and walk around.
Those cameras are very underpowered and won't go very far outside the house, even with like a +24dbi gain antenna you need to be close.