To super-size (or minimize) your webcam image, click Messenger and select "My Webcam."

Click Messenger again, and this time select Preferences.

At the top of the window that opens, click Camera Settings, where you can adjust the size of the image.

If you want to change image size for only one session:

Start your webcam by clicking Messenger, then My Webcam.

In the window that opens, click Webcam, then Image Size. You can pick Small or Large.