This site expains the mathematics behind images, and occasonally supplements with applets, animations, or teaching materials. Still a little sparse, but what is there is well done.
Project on blackboard. Trace/Connect max/min points with a smooth curve. Measure successive heights. Determine the rate of decay. Find the correct exponential decay function. Use graphing software to superimpose the function they find on top of the function draw on the board. Change parameters and repeat process. Could be worthwhile.