The truth, said Chrissy Criscitiello, is that she never gave a moment’s thought to the deal she was making when she posted pictures on Facebook. “They’re of me and my friends when we go out,” Ms. Criscitiello said. “My son’s graduation. My husband’s family reunion. A vacation we went on to Lake Wallenpaupack.

“I never thought they would be able to sell those pictures or give those pictures to someone else.”

In 2009, Ms. Criscitiello got a crashing introduction to the world of intellectual property, as the pictures and content on Facebook are called. On March 30, her sister Caroline Wimmer, 26, was murdered in her apartment on Staten Island. A month later, a reporter with The Staten Island Advance called the family home with news that a picture of her dead body had been posted on the Facebook page of one Mark Musarella.

As it turned out, Mr. Musarella, a retired police officer, was one of the emergency medical technicians who responded to the apartment when Ms. Wimmer’s parents discovered her body and dialed 911. He had taken at least one picture of her, and then uploaded it to his account. One of his cyberfriends informed the hospital where he worked of the picture, and he was immediately fired.

“I went right on Facebook, but by the time I got there, his account had been deleted,” Ms. Criscitiello, 34, said.