You can access the 'Select Region Button' through the 'Toolbar'.

Programs such as MSN messenger, Skype, PalTalk, ICQ, and others use the video resolution of 320x240 pixels to broadcast live video from your webcam. ScreenCamera also has that same video resolution in order to be compatible with these programs. So, when you click the 'Select Region Button' ScreenCamera lets you move around a 320x240 pixels rectangle and you have to do is click the mouse when you have positioned the region where you wanted. To select bigger regions simply keep the mouse clicked and resize the region you are selecting.