Gus Palmer (Kiowa, at left), side gunner, and Horace Poolaw (Kiowa), aerial photographer, in front of a B-17 Flying Fortress. MacDill Field, Tampa, Florida, ca. 1944. (Photo and caption by 2014 Estate of Horace Poolaw)

The photographs feature fish that have been specially treated to make the stained skeletal tissues visible through the skin and flesh. The technique, developed by Dr. Adam Summers, uses dyes, hydrogen peroxide, a digestive enzyme and glycerin to make the flesh seem to disappear. Photo: This image of the butterfly ray (Gymnura crebripunctata) helped scientists study the joints in its wings. (Photo by Adam Summers)

Shepherds lead their sheep through the centre of Madrid, Spain, Sunday, October 25, 2015. Shepherds have guided a flock of 2,000 sheep through Madrid streets in defense of ancient grazing, droving and migration rights increasingly threatened by urban sprawl and modern agricultural practices. Tourists and city-dwellers were surprised to see the capital's traffic cut to permit the ovine parade to bleat bells clanking its way past the city's most emblematic locations. (Photo by Daniel Ochoa de Olza/AP Photo)

A vehicle lies on a road in Adairsville. (Photo by David Goldman/Associated Press)

Marine researcher Tomasz Furmanek, 44, from Bøjarnesveien, Norway, takes stunning images while kayaking through various fjords and lakes in the Scandinavian country. During Tomasz’s free time, he works as a freelance photographer traveling around the lakes, fjords and coastal regions of the beautiful country – and capturing breathtaking photographs. Here: Hardangerfjorden, near Ullensvang. (Photo by Thomasz Furmanek/Caters News Agency)

Runner English Gardner poses for a portrait at the U.S. Olympic Committee Media Summit in Beverly Hills, Los Angeles, California March 8, 2016. “My musical inspiration when I'm training is usually a lot of upbeat music”, said Gardner. (Photo by Lucy Nicholson/Reuters)

It has taken 3,000 hours and 34 years to make – but the results are incredible. Artist Scott Weaver has created a huge but incredibly detailed model of San Francisco using 100,000 toothpicks. The work entitled Rolling Through the Bay also doubles as a marble run. Ping pong balls dropped on several ramps at the top of the model follow several “tours” through the city. They pass matchstick replicas of sights such as Alcatraz, Fisherman's Wharf, the Golden Gate Bridge and the city's trademark terraced houses on steep hills.

Saraa Mutawkil (R), 18, practises boxing at Al Rabie club in Omdurman May 10, 2016. (Photo by Mohamed Nureldin Abdallah/Reuters)