That was a fascinating read - thanks for posting.
It's interesting this isn't it. I have a small local history website, and often 'pinch' things found elsewhere (but mainly old things - so not presumably a worry). I try and credit where they came from, but sometimes I can't remember, or they themselves haven't any acknowledgements. I have also reproduced quite a number of old postcards and prints - and the copyright around these seems to be really hazy.
On the other side of the coin, quite a few of my own photos have ended up on other people's websites. I did recently contact the National Trust and pointed out that it was a bit cheeky for such a large organisation to be pinching my photo and not crediting me. They immediately apologised and put my name on it. My favourite was a photo of mine I spotted on a CD cover. The publisher was most apologetic and offered me a free CD.
You can probably guess why I turned down their offer!