How to select a rectangle
1. Open Window Clippings and make sure that “Prompt for selection” is selected. Now click the “Create screenshot” button.
2. Notice that the screen dims in preparation for your selection.
3. Simply hold down the left mouse button and drag the mouse pointer across the screen to create a rectangle. The resulting rectangle is highlighted to show your selection.
4. If it’s not quite right simply drag the mouse across the screen again to create a new selection. When you’re ready press the Enter key on your keyboard to capture the selection.