I think it's a great idea Tony.
If I had any I'd be happier for them to be 'out there' than in a draw which my executors will tip into a skip.

It'd be interesting to know how £much anyone had ever made from selling the photo of a folk singer.

There's a fairly interesting article here for anyone planning to copyright and sell their photos
https://medium.com/photography-secrets/how-much-should-you-charge-for-a-photograph-27f5ca0c965f

Presumably there is a date recorded by wiki which could be found by anyone interested in finding the original photographer.