This is a crop of a photo of Lena Söderberg, the centerfold of the November 1972 issue of Playboy. In 1973, engineers at the USC Signal and Image Processing Institute used it as a test image in their research. The data they collected from the image, specifically the red, green, blue color channel data, have become the standard benchmark for image compression quality ever since. That research also built the foundation for the image compression algorithms used in JPG and MP3s. It adds, I think, a nice resonance to know that the quality of much of what we listen to and see online is tuned to this fetching image. (two great geeky observations and articles on Lena here and here)