While you may think of server-side image maps as being limited in flexibility, you can actually identify complex shapes as image hot spots. Take a look at the following map file definitions, creating a rectangle, circle, polygon, and even an individual point.
#50x50 pixel rectangle starting at 0,0
rect /page.htm 0,0 50,50
#circle with 40 pixel radius starting at 50,50
circle /page.htm 50,50 40
#polygon with 3 vertices
poly /page.htm 15,15 15,75 50,45
#individual point-great for "easter egg"
point /page.htm 100,100