I remember when I first joined Dreamstime. One of the images I was most proud of was taken at a castle during my vacation in England last summer. I had uploaded it feeling quite smug because there were only a few other images of this particular castle, and mine seemed the brightest and (to me anyway) the most interesting. But I also kept getting this nagging feeling of doubt as to why there were so few images from there, given that it was not exactly an unheard of tourist destination.
And so I went back and did more research, and eventually realized it was actually private property and the owners actually lived there! I also managed to find my admission ticket, and sure enough on the back it said that no commercial photography was allowed without permission. Since it was clear to anyone who had ever been there, that the photo could only have been taken from within the grounds, I immediately disabled my image (which thankfully hadn't sold yet) to prevent any potential copyright issues arising. I tried contacting the email address provided on their website to find out their position on stock images of the property, but never received a response. And so even though I had other images I hoped to upload, I felt it prudent to simply keep them for my own personal enjoyment.
Out of curiosity I periodically do a search and I see that there are a growing number of photos from this castle property available on several microstock sites. None have any indication of having a property release.
Was I was overly cautious...perhaps even to the point of being paranoid...and could have safely sold the images I had taken there? Or are others, in their equal enthusiasm to potentially get sales on a nice shot of a tourist destination, not careful enough?