AVR-Chat

I need to measure the liquid level inside a transparent plastic 
bottle. I need to know when the liquid is below half bottle height and 
when the bottle is almost empty. Just two steps.
	The plastic bottle measures 12cm high x 8cm x 3cm.
	I'm not allowed to insert any probe in the bottle.
	There are four bottles side by side.

	I was thinking on metal plates mounted on each side of each bottle 
and using the capacitance method.

	Or a B&W video camera and some processing. I could generate four 
sample windows on each video line and integrate the samples. The four 
integrated signals would represent the liquid level on each bottle.
	An ATMEGA48 would do the level measurement with four ADCs.

	Comments, please.

	Thanks,
	Mark Jordan