When you do that, the picture has a "website"... http://blahblahblah.com/mysexypicture.jpg  

That is your picture URL.  Paste that into the appropriate field on the post, and your picture will appear in the post.  

...this board you'll find some discussions with posts mentioning other photo hosting sites. Don't use photobucket. They have issues with sexy, erotic, semi-nude, and or nude photos. They also have some policy about 3rd party use such as hosting the photo on their site and posting it here.