Why didn't people smile in old photos? For one, early cameras sometimes required a 15-minute exposure time, and holding a smile for that long was no small feat. But that's not the only reason Victorians donned dour expressions in photographs. Some avoided smiling because they were frightened by the process, since photo studios were often called "operation rooms." Others kept their mouths closed to hide their rotting teeth.

Instead of telling people to "say cheese," photographers quite literally instructed subjects to "say prunes" to make their mouths look smaller. Small mouths were considered more beautiful than a wide grin - and big smiles were associated with mental instability. The popularity of 19th-century death photos underscores just how differently people perceived photography. A photo wasn't a cheerful snapshot - it might have been the only remaining likeness of a loved one who had passed. Because of this, many treated photographs as somber, serious mementos.

What exactly made people start smiling in photographs? As it turns out, women led the smile revolution - with some marketing help from Kodak.

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