Hello

I already made a lot of websites with Joomla, and I would like to add a photogallery in one of them.

1 - Is it possible to integrate Zenphoto in a Joomla website, and, if yes, how (iframe ...) ? Do we use the same database or create a second one ?
2 - is it possible to give a login/pw to each client so that he can see only his own photos ?

1: We have had several people interested in Joomia integration. Unfortunately none who have followed through so far as I know.

So, yes it it would be possible to integrate the two systems, but it would require someone with Joomia development knowledge to make it happen. Of course you can always use the iFrame and/or custom Zenphoto theme approach. But you still have the question of single logon for your clients.

2: Please review our user guide, especially the section on user rights. What you want to do is achievable. The one restriction is that the client albums must be first level albums.

For completeness our article about that topic:
http://www.zenphoto.org/news/integration-with-existing-sites-and-other-cms