If you notice some poorly dressed guys wearing fanny packs outside of your house snapping photos in the near future, don't worry, they aren't terrorists; they're Canadians. A Canadian company called Zaio is in the process of photographing every single house in America to then sell to banks, insurance companies, and appraisal firms.
Creepy? Yes. Illegal? No, not unless they're actually on your property when they take the picture. Would you be more OK with this if they were taking photos for some sweet 3D map you would eventually be able to use on the Internet, or does the reason not matter? My advice: paint a giant "Canadians Go Home" sign and put it over the front of your house. That'll show 'em!