HI, I installed Zenphoto and I am very happy with it.
There is one thing I would like to ask if it is possible or I am missing it .....

I would like to have Upload button within the album window where my users can upload photos without going into the admin screen. Is that possible ?

Thank you !

We don't provide such a function and they would have to login anyway. Front end usage is always easily in danger of security issues.

If you are refering to logged in "registered users" then there will be an upload link in the album page admin toolbox that they will have on their page. If for the general public, the acrylian's answer stands.