Your images are sorted on the server privately. They are not shared with anyone else. You're given a uniquely generated url which you can use to share the image with whoever you wish. The images will be hosted on the server for a while and will be deleted if they're totally inactive after a period of time.

The main addition to the pro version is that you'll be able to set the software up so it uploads to your own web hosting account in a folder you specify. That way you can have total control over your images.

All this "15 mb per ip" stuff gets complicated.