Articles & events are pretty much out of the box - you just setup a membergroup with the appropriate privileges and a weblog for the content to go into. You would set the default status to pending, and setup an email notification for when new posts are submitted. You could either have them use the Control Panel or create a stand alone entry form for the purpose.
For photos, there is no out of the box stand alone entry form. If you want them to use the EE gallery you’re going to have to let them into the Control Panel and have access to creating new gallery categories etc.
Otherwise you could roll your own gallery using the weblog module and follow a similar approach as above.