I understand. I'm suggesting you use the built in functionality for image attachments as a way for the friend to view the image in a frame, with your elements added in. If you still need this functionality as is, you can at least use it for inspiration for your own new functionality. You could also use the rewrite API for implementing more elegant permalink like link.
How is the link sent to the friend. User cut/pastes to his messaging method of choice? E-mail from your server? Open the user's default e-mail with link already in body? Offer several options?
Finally, edit a copy of the content-image.php template to grab the data attached to the URL and display it in the correct place on the page.
All this is too much to get into any detail. You also have a few design decisions to make on exactly the best way to implement each detail. I suggest starting with something basic, like clicking a button that displays just the image attachment link. Then start adding more functionality, one small step at a time. If you get stuck anywhere, come back here with a specific, detailed question. Right now, your question is too broad and general to answer with any more detail than I have right now.