I was starting to get some advertising contracts for different photos I had taken long before I ever considered they could make money through selling or advertising. One company that wanted to use my "row homes" image for advertising asked if I had received permission from the house owners to use the house in an ad they were putting together. The picture was old and lower resolution anyway and I took it upon myself to go back to the location and rephotograph the subject in South Baltimore.
I had the documents with me to sign for permission to photograph the house and I knocked on one of the row house doors. A lady answered through the screen door and when I went through the spiel of asking for permission of photographing her house along with other row homes she said, "I don't know, I'll have to get my mother.". I waited outside for what seemed like five minutes and finally the daughter came back with a very elderly lady. I again went through the spiel as nicely as I could. She replied, "No, I don't think so".
This was just the first house... I needed to get permission from the other houses in the shot as well. I never even got the opportunity to use the permission documents. There was nothing more I could think of to say standing out there on the street talking through a screened door, so I paused for a while and said, "Ok then... thank you".
I really expected about as much but I had to try at least once.
There's an old expression... "It's easier to ask for forgiveness then to ask permission".
Generally, if you're taking photos from a public area, you're ok, but if you use those images for advertisement and/or to make a monetary profit, that's when you need to be careful.
The contract go-between actually wanted my original shot, not the new higher resolution image I offered them. They told me, we'll make it a different color or something.
(I suggest to make this thread private if this is the direction we're headed in the thread.)