Back in the late 1990s my cousin Brad was a big fan of the music group Savage Garden, so much so that he had the following image as his computer desktop wallpaper:
I often had access to Brad's computer files as I would frequently bring over a ZIP disk and install add-ons for Duke Nukem 3D or get a copy of a level he had made, so it was easy to get a copy of the above image, edit it at home, then later copy it back to his computer while he was out of the room for a minute. Below is the replacement image I put on his desktop:
I can't remember how long exactly, but it was at least several weeks if not a few months before Brad noticed. (I didn't overwrite the original image, so no harm was done.) Savage Fartin’ would of course have been more correctly, ah, spelled, but I thought it might have been too obvious to the unobservant eye.