Reproduce the "Talk to the the hand" Gesture and allow the user to customize the message and the background picture.
Once you pick your background picture and/or enter your message, just reproduce the gesture of "Talk to the hand" and the message will be blown out on the screen!

Note:
This is currently offer free, as I am still adding features to it so stay tuned and download it for free while it last. Remember your update will still be free!