User Log in and Register

I want people to come to my site register and log in to my site. Once they register I want them to be able have a front-end platform to post articles images and such related to the categories I have already set up. however, I want to have some kind of control as well to what will be accepted on the site in other word a filter. It will filter spam, or anything that is not related to my categories. in other words i don’t want users to register, and post about porn, or stuff like that.

So my site will be open to the public. However, I also want them to have restriction on picture resolution. I dont want them to be up;padding supper high images that are not necessary.

I need help, please help me.

here is my site as it is now. http://www.Brainolo.com

HELP HELP some one.