If you take a flash photograph of a child, and one of his or her pupils looks white in the resulting image, it can indicate an eye tumor. In the U.K., a series of ads uses reflective ink to illustrate that warning sign, in the hope of teaching parents how to recognize it.
The ads, located at doctors offices and day care centers, feature kids who actually survived retinoblastoma, a rare but potentially fatal form of eye cancer that in most cases affects infants, toddlers and young children. If you snap a flash picture of the poster, you can see what to watch out for in pictures of your own kids.
Childhood Eye Cancer Trust, aka Chect, is the nonprofit group behind the campaign. Agency Wunderman created the ads. There's also a social component—Fast Company has more details on the awareness push and the production process.
It's an incredibly smart, simple use of media, given how many people carry smartphones, and the fact that early detection can save a child's life or eyesight.