In this November 28, 1966 file photo, one of the 10 beagles involved in the first test of the Veterans Administration Hospital in East Orange, N.J. smokes a cigarette through a machine linked to its windpipe by a plastic tube to test any link between smoking and emphysema. (Photo by AP Photo)

Tank crew standing in front of M-4 tank, Ft. Knox, Kentucky, June, 1942. (Alfred Palmer/OWI/LOC)

Artist Marco Ugolini Per Color series of photographs display supermarket products divided by colour. The Images taken by Brazilian photographer Pedro Motta, were created for Marco's residency at JACA the Center for Contemporary Arts in Brazil.

Takehiko Yagi is a rising star in Japanese photography, and his vibrant pictures of the Hindu spring festival of Holi won the Grand Prize at the fourth annual Nikkei National Geographic Photo Prize. Diving into the Colors of Holi is his first exhibition in the US, on show at Foto Care Gallery in New York until 28 September, 2016. Here: Jaipur, India, 2013, (Photo by Takehiko Yagi/The Guardian)

A photographer has taken an explosive set of images by igniting gasoline in midair. Rob Prideaux, 45, photographs fire and smoke and then creates patterns from it. The San Francisco-based artist captures the fire in the split second its visible by using highly arcane methods. Rob's Smoke and Fire series is his quest “to shape one of the more uncontrollable phenomena in nature”. (Photo by Rob Prideaux)

Physicist Arie van't Riet uses a series of duel X-ray cameras to capture flowers, plants and small animals in living dioramas. The x-rays are then finished and colorized in Photoshop. Giving way to some breathtaking nature scenes. Photo: “Chameleon and Begonia”. (Photo by Arie van't Riet)

These are the spectacular snaps of swirling star trails which transform the night sky into a kaleidoscope of color. Keen photographer Evgeniy Zaytsev, 24, captured the stunning shots on trips to Crimea, Altai and Murom, Russia. The pictures of circular star trails are formed by merging multiple photos taken over the course of several hours. Movement of the Earth causes the stars appear in different places in each image. Here: vibrate, colorful star trails over an abandoned beach house. (Photo by Evgeniy Zaytsev/Caters News)

Participants are covered by colored powder as they compete in The Color Run, a five-kilometre untimed race, in Hanoi, Vietnam September 26, 2015. Approximately 7,000 participants took part in Hanoi's first Color Run, reported local media. (Photo by Reuters/Kham)