1The only known image of Albert Einstein working on his theory of relativity
In 1934, four hundred lucky students in Pittsburgh watched as Albert Einstein mathematically derived his famous mass-energy equivalence equation: E=mc2. What you see above is the only surviving photo from that lecture. It was pulled from a halftone newspaper clipping by David Topper and Dwight Vincent of the University of Winnipeg, who discovered it in 2007. The famous equation is on the blackboard to the right.
2The only known photo of Billy the Kid with the Lincoln County Regulators
There is only one known photo of Billy the Kid (William Henry McCarty, Jr.) that was authenticated—until October 2015 when a second photograph of the outlaw was verified as authentic. It was bought for $2 at a Fresno junk shop seven years ago and could be worth $5 million.
The 4-by-5-inch tintype shows the Kid, and several members of the Lincoln County Regulators, playing croquet with friends, family, and significant others in the summer of 1878, according to Kagin's Inc., a numismatic firm that specializes in U.S. gold coins and collectibles.
Jeff Aiello, executive director of the documentary entitled Billy the Kid - New Evidence says, "This is the first photograph ever discovered of Billy the Kid with The Regulators, and that's significant in American history."
3The only known photo of one of 272 Georgetown University slaves who were sold to the state of Louisiana
In 1838, Georgetown University in Washington, D.C. sold off 272 human beings to the state of Louisiana to wiggle itself out of debt. The mass sale of the men, women, and children was especially troubling—even at that time. Two Georgetown Jesuit presidents negotiated the transaction that earned the college $3.3 million in today's dollars and used about $500,000 of it to settle Georgetown's debts.
The photo above is the only known photo of a man named Frank Campbell, who was one of the 272. Campbell was enslaved on a Jesuit plantation in Maryland. In 1838, he was shipped to a sugar plantation in Louisiana along with many others who were sold to raise money for the university.
4The only known photo of the musician known as the "Father of the Delta Blues"
Charley Patton is considered by many to be the "Father of the Delta Blues, " and this 1929 Paramount promotional still is the only known photo of him.
Patton would sometimes hold the guitar on his lap and play it like a zither, as seen here. His wardrobe caught the eye of historian David Evans—Patton's collar and lapel are curiously hiked up on his left side, which may have hidden the scar on his neck from a near-fatal razor attack earlier that year.
5The only known photo of George & Willie Muse, who were kidnapped and forced into the circus, with their captor
George and Willie Muse were abducted from Truevine, Virginia, and forced into the circus. The brothers, albinos born of African-American parents, were falsely told that their mother was dead and that they would never be returning home. While there are many photos of the brothers, this is the only known photo of George and Willie with one of their captors, showman Al G. Barnes of Ringling Bros. and Barnum & Bailey Circus.
In 1927, while visiting their hometown, their mother finally tracked them down and threatened to sue the circus. The Muse brothers were freed before returning to show business on their own terms a year later.
6The only known image of Marilyn Monroe, President Kennedy and brother Bobby Kennedy together
The photo above, of actress Marilyn Monroe, then President John F. Kennedy and brother Bobby Kennedy was taken in May 1962 after Monroe's famous "Happy Birthday" serenade to the president.
The black-and-white photo, taken by White House photographer Cecil Stoughton, showed Monroe still wearing the infamously tight-fitting dress she wore when singing earlier at Madison Square Garden.
Filmmaker Keya Morgan owns the original and says, "There is no other known photo of Bobby [Kennedy] with Marilyn or JFK with Marilyn, and it's not because they were never photographed together. In fact, they were photographed together many times, but the Secret Service and the FBI confiscated every single photograph."
Stoughton, who sold the image to Morgan a year before his death in 2008, told him agent missed one negative in their search. "The Secret Service came in when he was developing the negatives and confiscated all the ones of Jack, Bobby with Marilyn. The only one that survived is the one that was in the dryer."
7The only known image of El Santo unmasked
Rodolfo Guzmán Huerta is arguably one of the most famous men in the history of Mexico, and yet, few people know his name and even fewer know his face. The silver faced "luchador" known as El Santo had only once partially removed his mask while in public—during an appearance on Contrapunto, a popular Mexican talk show. The above photo is the only known image of El Santo unmasked.
8The only known image of Jocelyn Gordon Whitehead—the man who killed Houdini
This is the only known photo of Jocelyn Gordon Whitehead, the McGill University student who dealt the fatal blow to magician Harry Houdini in his dressing room at the Princess Theater in Montreal on October 22, 1926.
Whitehead's blows to Houdini's abdomen either started, contributed, or covered-up the appendicitis that would take Houdini's life nine days later on Halloween.
Whitehead, who is holding a book, had a strange history with them—he gained access to Houdini's dressing room with the claim of returning a borrowed book and was also charged with shoplifting books twice in 1928. He died a recluse and hoarder in 1954.
9The only known photo of the real military officer who was the inspiration for the lead character in The Legend of Sleepy Hollow
While author Washington Irving did not readily admit that the lead character in The Legend of Sleepy Hollow was named after Colonel Ichabod Crane (above), the two men had met before. They both served at Fort Pike, Lake Ontario in Sackets Harbor, New York. Irving was an aide-de-camp to New York Gov. Daniel D. Tompkins at the time.
10The only known photo of the first African American man elected to the U.S. Congress
This is the only known photo of John Willis Menard, the first African-American man elected to the U.S. Congress. Menard won a special election for a House seat in Louisiana representing New Orleans in 1868 but was challenged by his opponent, Caleb Hunt. He went before the House of Representatives to appeal his win and was the first black person to address the House of Representatives. Menard was considered unqualified and never took his seat—the position remained vacant until the next election.