OK, thanks.
I don't want to spend my life with admin, so I would be tempted to sell the images to the client, for them to use them as they want, for as long as they want.
So, if I get a killer shot, and give it to the client on a long licence, they could use it as they want (or sell it on) or I could do the same (as I own the copyright.........?)
Is it fair to state in a licence 'you cannot sell this image on'? If so, I'm not sure how that works for me. I do a lot of work for Architects (they pay me) but they use the images on behalf of their clients (so they are in effect selling the image on, to their clients) which I don't have a problem with.