Hidden Camera Pranks & Gags, Instant Author Signing Book

Are you an author, your are not but here in this situation y'll be an author for a moment, lets say an instance author. Imagine that one upon time you were in a library and some one comes to you to sign at the book you don't write and you are not also the author of it but the most stunning thing is your photo is on it , so what you will do in this situation?!! lets see :)