There is already a skin object that handles the login/logout link.Custom registration fields can be done with the framework already. I'm not sure about uploading an image but I'm pretty sure there's a 3rd party module that has that ability if you don't want to code it yourself. You mean after every time they change the image? This would probably require a custom trigger. If you just mean on registration then setting the portal on Private requires the administrator to authorize the account. Not sure what you're asking here