private property on the internet.
as far as i'm aware if your not claiming it to be your own and/or making money from it, you should be fine, if the owner claims its private it shouldn't have been put on internet, ive robbed many photo's over years for personal use and thats fine, ive also had people use my photos of models over the years some have asked some havent but i always thought WOW someone else likes my photo.
however the interwebs is a strange place and some people are better than others.