I understand this. But looking at Photopost, it has basically all the features for this in place already. I only forward here, what my users want to have.
The only thing which is missing, is a kind of image, which is invisible and does not show up on the index page. As far as I can see it, there is a hack out there for not showing photos of a specific category on the idnex page or in subcategories. This would be the kind of solution I am looking for, although I have not tested that hack yet.
I do not want to replicate a forum. But in my photoportal, many users do not want to register in a forum. They only want the photo gallery and within this photogallery they want to ask questions about photo retouching etc.