It looks like an American Airlines Boeing 767-200
http://www.airliners.net/info/stats.main?id=103
This means that the aircraft is 155 feet long (47.2 Meters).
If we can find a way to mark the same distance on the ground we could then use some basic trig to calculate the altitude. Unfortunatly the shadow is no good because it is fuzzy and distorted by the angle of the sun.
Does anyone know of a way to find the scale on the ground? Maybe this can be found by measureing the length of a known object such as an 18 Wheeler truck on the road.