In July the Internet exploded with a photo of schoolchildren. The kids, dressed in dark shorts and colorful T-shirts, appear to be enjoying a field trip, perhaps to a zoo or a nature preserve. In the center of the image, a crouching girl in a yellow T-shirt holds a medium-sized turtle toward an adult taking a picture of the scene. Smiling classmates, dressed in matching white, green, red and blue T-shirts, gather around the girl and turtle. At first sight, nothing seems amiss in the group shot. But a closer examination reveals that the many hues in the background and the children’s clothing are not real colors. The seemingly polychromatic image is actually black-and-white, overlaid with a thin multicolored grid.