If you've had kids, you know the drill: Every fall or spring, your child would come home with an order form for school portraits. You'd pin some money inside your little one's backpack and several weeks later, he'd trot home clutching the photos. School photos go back to the early days of photography when, in 1840, Yale class of 1810 alumni posed for the camera.

Some school images are easily confused with photographs from events such as weddings. For instance, in the late 19th and early 20th centuries, young women dressed in white for graduations. A rolled-up diploma indicates a photo of an ivory-gowned woman isn't a bridal portrait.