People feed the birds in Battery Park in the Manhattan borough of New York, December 18, 2014. Hart has been feeding the birds three times a week for the last three years. (Photo by Carlo Allegri/Reuters)

A labourer packs incense in preparation for Tet, the traditional Vietnamese lunar new year, in Hong Chau village, outside Hanoi January 29, 2015. Tet is from February 14 till 24. (Photo by Reuters/Kham)

A runner taking part in the 38th Annual Empire State Building Run-Up is pictured arriving on the 86th floor in the Manhattan borough of New York February 4, 2015. (Photo by Carlo Allegri/Reuters)

Artist Vik Muniz is known for his gigantic composite installations and sculptures created from thousands of individual objects. In this new collaboration with artist and MIT researcher Marcelo Coelho, Muniz takes the opposite approach and explores the microscopic with a new series of sandcastles etched onto individual grains of sand.

Meet the star students of orangutan school – the unique rehab centre where orphaned apes are taught how to climb trees and survive in the wild without their mum and dad. (Photo by Caters News)

Revelers celebrate the Indian festival of Holi on a boat cruise around part of Manhattan on March 17, 2012 in New York City. During the Hindu festival of Holi, also known as the Festival of Colors, which marks the arrival of spring, participants throw colored powder and water on one another. Many of the New York participants are Indian-American. (Photo by Mario Tama/Getty Images)

A two-horse team street cleaner, with sprayer, squeegee, and roller at rear. New York, between ca. 1910 and ca. 1915. (Photo by NYC Municipal Archives)

The stunning shots capture the moment a female bear and her two cubs enjoyed the last warm rays of the sun at the Arctic National Wildlife Refuge in Kaktovik, Alaska. The bears can be seen gazing at the vibrant sunset and appear to revel in the tranquil moment as they bask in the array of colors. (Photo by Sylvain Cordier/Caters News)