Li Yuming, a local farmer who is interested in scientific invention, works on his unfinished miniature submarine “Xiaguang V” on the outskirts of Wuhan, capital of central China's Hubei province August 24, 2007. “Xiaguang V”, which is 3-metre long, 1.2-metre in height, has a maximum diving depth of 20 metres, and can hold two adults and one child at the same time. The submarine will be used for tour after safety test, local media said. (Photo by Reuters/Stringer)

KALTENBERG, GERMANY - JULY 08: Actors dressed as knights perform during the traditional Kaltenberg knight tournament on July 8, 2007 in Kaltenberg, Germany. With around 120,000 visitors each year, the festival including knight tournaments, medieval styled markets and a variety of music performances, the event is one of the biggest of its kind. (Photo by Johannes Simon/Getty Images)

An activist of the anti-G8 forum “Block G8” shows his middle finger to a police helicopter passing overhead June 07, 2007 at Bollhagen, near Heiligendamm, Germany. (Photo by Carsten Koall/Getty Images)

A tiger yawns next to a piglet at the Sriracha Tiger Zoo, in Chonburi province, Thailand, June 7, 2016. (Photo by Chaiwat Subprasom/Reuters)

Young U.S. visitors pose for a photograph next to a vintage car in Havana March 16, 2016. (Photo by Ueslei Marcelino/Reuters)

A youth skates next to a road in Palembang, South Sumatra, Indonesia on August 15, 2018. (Photo by Edgar Su/Reuters)

“Freedom”. After the 30 years banning import large motorcycle, in 2007, the Taiwan government reopened the import licensing of the motorcycle displacement over 550 cubic centimeter. Those large bikes, which were never seen before, were strange thought and treated unequally frequently. However, those adversity will not stop those enthusiastic bike riders from chasing the road of freedom. Photo location: Taiwan. (Photo and caption by 火花 羅/National Geographic Photo Contest)

The contest began in 2007, and since then photographers from more than 70 countries have entered. Photo: Michael O'Neal of San Francisco won first place in the animals category in the 2014 iPhone Photography Awards. (Photo by Michael O'Neal)