And, to answer your question, you can't "get" one. Only mods can create stickies and they can do that for you if you ask nicely and they think it's worthy.
If you attached a pic to your post in a thread , go to the post there and find an option Edit at the bottom of the post. If you click this, you get the post for edition open an there you may delete the attachment.
If you're using a hosting service, simply define the photo as "private" using the hosting editor. You will retain the pics, and can make them public again at any time, but so long as they're kept "private", they will not show up on any post you've made.