pre-draw the constant, non-changeable parts of your sketch as a template that you can use and reuse
In some situations, you will be responsible for modifying only a portion of an existing visual interface. Certain portions may be pre-determined and fixed, either because of the shape of the hardware product (e.g., a cell phone body, buttons and screen size), the application hosting the system (e.g., a web browser frame), a window that contains pre-existing controls and information (e.g., an application), or a layout/style sheet that dictates how the contents of a window must conform to a certain layout (e.g., dialog boxes, particular web pages).
• a photo, screen grab, or found image of an existing visual
• an image ...