I too am very confused about Property Releases in respect of what does require a release and what doesn't.
Shorly I'm off the the Solent (Portsmouth, UK) to photograph a Second World War restored motor torpedo boat from another boat.
Alamy state that I will need a Property Release as the boat belongs to someone despite it being in a public place.
So going by that premise, if I take an image of a city skyline, then I need a Property Release for each of the buildings in the image as each one is owned by someone.
It just doesn't sound right to me as I was under the assumption that