The competition has amassed more than 440,000 entries in the 16 years it has been running, with submissions flying in from all over the world.
There are six categories in this year's contest, including "natural world", "the American experience", "travel", "people", "altered images" and "mobile".
A stormy shot of snow-dusted peaks in China, an intimate moment between an indigenous couple in Mexico and a candid capture of a US marine corps soldier leaving a gas chamber are among the eye-catching entries so far.
Here MailOnline Travel serves up a selection of photos vying for the number one spot. The 2018 competition closes on November 30 and the winner will be announced next spring...
Photo / Callie Chee
Callie Chee from Australia took this powerful shot, titled "The King". The image shows Yulong Snow Mountain in Yunnan, China, after a heavy snow storm
Photo / Roxanna Ortiz
A US Marine Corps recruit exits a gas chamber at an army camp in California. Roxanna Ortiz, who took the image, notes that the gas chamber trains recruits how to use gas masks so they can respond to potential chemical and biological threats
Ruben Escudero from Mexico took this touching portrait showing a couple after solar electricity was fitted in their home. The photographer explains: "Faustina Flores Carranza, 66, and her husband Juan Astudillo Jesus, 63, sit in their solar-lit home in San Luis Acatlan, Guerrero, Mexico. Faustina and Juan have seven children and have been together for 48 years. Like many members of the indigenous community, they have never had access to electricity. When asked how having solar has impacted their lives, Juan said, 'For the first time, we are able to look each other in the eyes in our moments of intimacy'"
Photo / Reiko Takahashi
Reiko Takahashi, from Japan, photographed the watery remains of the USS Emmons in her watery grave of 80 years in the sea of Okinawa
Photo / Danie Ferreira
Danie Ferreira from South Africa took this candid shot of a mother polar bear nursing her cub. He said she was on an extreme expedition in east Greenland and travelling by dog sled with locals when he spotted the tender moment
Photo / Harry Skeggs
Harry Skeggs from London said he was exploring Ranthambhore National Park in India when he spotted a Bengal tiger "peering mysteriously though the foliage"
Photo / Maria Plotnikova
Maria Plotnikova from Moscow, Russia, titled this shot taken in Havana, Cuba, "nternetization". She explained: "Currently in Cuba, all internet services are controlled by the state-owned telecoms company ETECSA, and internet access in private houses is practically inaccessible. Recently, however, the situation has begun to change. With WiFi hotspots popping up across Cuba's major cities, Cubans finally are beginning to embrace the internet revolution, more than ten years overdue"
Photo / Julio Castro Pardo
Julio Castro Pardo from Spain took this picture, which traces the Milky Way over the skies of Asturias, between the lakes Ercina and Enol in the Picos del Europa
Photo / Callie Chee
Callie Chee from Australia took this striking image of women from the Karen tribe on the Myanmar side of the Thai border. She explains that the females are best recognized for their elongated necks, with heavy brass rings around their necks and forearms
Photo / Russ Allison Loar
Russ Allison Loar took this colourful image of his wife, Cheryl, at one of the few 1950s diners left in southern California
Photo / Ruben Escudero
Ruben Escudero took this photo titled "Reflections in Lesotho", showing a boy with a baby donkey. He explains that in Lesotho, which is a landlocked country in southern Africa, most small farmers can't afford tractors or motorised transport so they rely on donkeys for transport and to help cultivate crops
Photo / Pim Volkers
Pim Volkers from the Netherlands took this dramatic shot of wildebeest crossing the Mara River in Tanzania. Commenting on the photo he said: "We decided to rise very early to be there before sunrise with the hope they would start crossing with perfect light conditions. And so they did..."
Mioara Chiparus took this photo of her hostess, Ekaterina, who looked after her in a sleeping cart while travelling on the Trans-Siberian train route from Moscow to Vladivostok
Photo / Willem Kuijpers
Willem Kuijpers from the Netherlands took this candid black-and-white shot in Siciliy, Italy. He said that he took it at the end of a 24-hour holy Friday procession in Trapani, with these women weeping as the statue of the Madonna mourning was carried backwards into the church
Photo / Alessandro Sgarito
Alessandro Sgarito from Rome took this photo while travelling in Hong Kong. He titled the shot "Divas" and said he looked on as he watched two women striving to get their best pictures one sunny afternoon
