I mean can "users" upload pictures to a post without Admin-rights ?
Many of them are not comfortable with a computer,
so its best they dont know about the administration-panel.
Can WordPress do something like that ?
In phpBB only a few are Administartors, the rest are users,
and have rights to create post upload photos.
But how can I do something simulair in WordPress ?
First WordPress and phpBB are two different beasts. If you're looking for a forum plugin to equal phpBB, you may not find anything that is it's match. But there are several forum plugins for WordPress.
bbPress (very limited in what it can do):
Mingle Forum (a bit more functionality than bbPress)
Simple:Press (almost as much functionality as phpBB)
If you really want to have a more modernized community site, you should look into BuddyPress:
But if a user got the rights to edit posts and adding pictures,
then it will always be done in the admin interface, right ?
Maybe I sould install a forum instead, but I dont know if its easily to add photos in post on a forum plugin.
All of the above plugins (except bbPress) will allow regular users to upload images, etc. without using the admin interface. bbPress will, with the addition of an additional plugin, as bbPress was designed to be very lightweight.