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Notes:
The clickable regions are the balloon, the title block in the bottom right, and the circle containing the portrait. The remainder of the image also has a default link set. These demonstrate the polygon, rectangle, circle and default shape types, respectively.
The left and right eyes of the figure in the portrait are overridden; one to make the area unclickable, and the other to specify a different link. This demonstrates the ability for one shape to override a subset of another's area.
Image: Postcard titled “Descente de Jacques Garnerin en Parachute” (1797) (Wikipedia)