What is the difference between a picture and a photograph?

Pictures are photographs that are framed, and therefore properly developed. "Picture" is the more generic term, and includes any kind of visual representation, whether it is drawn, painted, photographed or produced by some other means. You could even call a naturally produced image a "picture". The Word picture can even refer to a memory or mental process that is by nature completely immaterial. "Photograph" virtually always refers to a physical image created with chemical or digital imaging technology.