There's a reason people are uncomfortable with strangers taking pictures of their home. Its rude. A vehicle taking pictures for assessment should be properly marked ditto those from the insurance company. Anyone else should knock on the door and ask.
My husband is an appraiser and he owns his own company and drives a personal vehicle for that job. It's not marked with anything saying his company name or what he does for a living. He's certainly not going to go around and knock on the doors of every house he's using as a comp, just doesn't have time. He never even gets out of his car, just stops in the street and snaps a picture. Nothing wrong with that.
Heather
I'm going to continue to patronize businesses whose employees don't skulk around in unmarked cars. A door magnet only costs a couple bucks. There isn't a good excuse for using an unmarked vehicle. A short conversation with a homeowner is a much better use of time, than say.... a couple hours at a police station.
The first time I called about someone taking pictures on our street, they were casing a house of a gun collector. The police weren't able to do anything to stop the robbery, but after they had a nice description of the man, his car and his plate number. You know who I didn't report to the police? The properly marked assessor's vehicle and the guy that said he liked our mail box.
You know who our nighbour reported? A Real Estate Agent in an unmarked car taking pictures. After they found the first guy with the guns Mr. Real Estate Agent got to spend some time with the police, explaining his suspicious activity. Was his activity legal? Yes, well as soon as he could convince them he wasn't in cahoots with the guy stealing guns, then it was legal.