A police officer stands at a police cordon near the scene of a terror attack in London, U.K., on Sunday, June 4, 2017. A van swerved into Saturday-night crowds on London Bridge, before three men got out and went on a stabbing rampage through nearby bars. (Photo by Luke MacGregor/Bloomberg)

Medic James E. Callahan of Pittsfield, Mass., gives mouth-to-mouth resuscitation to a dying soldier in war zone D, about 50 miles northeast of Saigon, June 17, 1967. Thirty-one men of the 1st Infantry Division were reported killed in the guerrilla ambush, with more than 100 wounded. (Photo by Henri Huet/AP Photo)

Men carry a dog, wearing a costume and seated on a stool, as a form of respect as they believe that dogs found water for their ancestors, during a local festival for the Miao ethnic minority in Jianhe county, Guizhou Province, China, August 14, 2016. (Photo by Reuters/China Daily)

Two men push a classic Messerschmidt KR200 “Kabinenroller” at the 7th Cairo Classic Meet in Cairo, Egypt, 23 March 2019. The exhibition for classic cars is held at the Smart Village in Cairo. The exhibition is held to exchange experiences in how to preserve the old cars, and also for promoting tourism. (Photo by Mohamed Hossam/EPA/EFE)

Pascal Martinot-Lagarde, of France, celebrates his bronze medal in the men's 110 meter hurdles final at the World Athletics Championships in Doha, Qatar, Wednesday, October 2, 2019. (Photo by Petr David Josek/AP Photo)

Jack London was a prolific photographer in addition to his writing. Here: Salvation Army barracks in London during Sunday morning rush – men who had been given tickets during the night queuing for free breakfast, 1902. (Photo by Jack London/Courtesy of Contrasto)

Police investigators inspect the bodies of two men lying on a sidewalk, who police said were killed after a drug “Shabu” (Methamphetamine Chloride) buy-bust operation in Quezon city, Metro Manila Philippines, October 9, 2016. (Photo by Ezra Acayan/Reuters)

Men carrying a shrine jump over a bon fire, which means a wish for good luck during a traditional Chinese lunar new year celebration in Jieyang, Guangdong province, China, February 2, 2017. (Photo by Reuters/China Daily)