Lidar image from 3300 feet of NY ground zero
Remote sensing tutorial
A 2004 discussion of one millimeter per pixel resolution for Very large scale aerial (VLSA) imagers
Google earth has some aerial photos with 3 inch (7.6 cm) per pixel resolution
Foreign governments fear the high resolution pictures of sensitive buildings available to the public
Wikipedia talks about google maps and competing services. One service is Amazons A9 with van level pictures. Systematic pictures taken from the side of automobiles.