Shortly after the invention of photography, tinkerers did their best to manipulate photos into novel formats. Stanhope devices were developed in the mid-19th century, after inventor John Benjamin Dancer began printing microphotographs onto glass slides. In Paris, commercial photographer René Dagron saw the potential of Dancer’s miniature images, though Dagron knew they were out of reach for most people because the tiny photos required an expensive microscope to view them.

In 1859, Dagron patented the first Stanhope lens mounted with a mini-photograph—named after the magnifying device invented 50 years prior by Charles, Third Earl Stanhope. Dagron improved his device the following year to create the Stanhope as we know it today.

A small glass cylinder had one end ground into a convex form, and a tiny, translucent photograph was mounted onto the opposite end. When the Stanhope was held to the light, this microphotograph was visible to the naked eye, through its curved lens.

This miniature lens could be inserted into all manner of ordinary objects—jewelry, pocket knives, watch fobs, needle cases, letter openers, thimbles—making them perfect for hiding images in plain sight. The photographs embedded in these Stanhope devices ranged from postcard-style landscapes to views of historic events, from mundane product advertisements to sexually explicit subjects.

Within a decade the fad had exploded and Stanhopes were sold at popular tourist destinations and novelty shops all over Europe and the United States. Dagron continued to develop more efficient ways of printing microphotographs and manufacturing Stanhope lenses. In fact, the original factory he built at Gex, France, continued producing lenses up through 1972, when the novelty appeal of Stanhopes had finally worn off.