I can see how this happened. It was spotted by someone driving behind a coke truck. I bet it was less obvious in smaller sized posters but when it was blown up to giant size and put on the back of a coke truck, suddenly you clearly see it. And once you see it, you’d easily spot it on smaller renditions of the artwork. I bet the artist hadn’t taken the sizing up into account. Wouldn’t have been an issue if the artist hadn’t snuck the image in in the first place but I can see how a whole campaign launched before it was caught.