Coming back on what I posted earlier.
Maybe I'm too relaxed about this issue. But I feel the enormous advantages of being able to post digital photos on the Internet far outweigh this unpleasant downside.
I love posting my photos, and I get enormous pleasure looking at other SP'ers photos. There are sights here I would never, ever have got to see. Some of those winter exposed ridges!
Just keep them low res and no one can use them for any serious alternative purpose, they have to come to you for decent versions.
Incidentally I have used other peoples' photos for some of my web sites. (steam locos.). And with the exception of the UK, (miserable tight fisted so and sos over here), have always been granted permission. Apart from one 1930s German steam photo I really wanted to use, where I went to enormous lengths to try and find a copyright owner and having failed, put a note to that effect under the photo when I used it.
The USA has been the easiest place to get permission from! One book company had an old photo in one of their books I really wanted to use, but they had lost details of the copyright owner. So they gave me appropriate wording to use under it, which was very kind and thoughtful of them.