Photographer Andy Hall joins the thousands of fans from west Africa who have gathered for Baaba Maal's annual Blues du Fleuve festival in Senegal. Here: Dancers wait to perform on stage. (Photo by Andy Hall/The Observer)

A passenger not wearing pants sits in a subway train during the “No Pants Subway Ride” in Prague, Czech Republic, January 10, 2016. The event is an annual flash mob and occurs in different cities around the world in January, according to its organisers. (Photo by David W. Cerny/Reuters)

Visitors walk past a family of scarecrows during the Scarecrow Festival in Heather, Britain July 29, 2015. The annual event asks residents of Heather to make scarecrows to raise thousands of pounds for local groups and charities. (Photo by Darren Staples/Reuters)

Women dance in costume during the West Indian Day Parade in Brooklyn, New York September 7, 2015. The parade, which takes place annually, celebrates Caribbean culture and history. (Photo by Andrew Kelly/Reuters)

Pupils participate in a calligraphy contest to celebrate the New Year in Tokyo January 5, 2016. Over 3,000 calligraphers who qualified in competitions throughout Japan wrote resolutions or wishes onto paper sheets during the annual contest that marks the start of the new year, according to organizers. (Photo by Thomas Peter/Reuters)

A participant, called a musher, races in the 33rd Aviemore Sled Dog Rally in Aviemore, Scotland January 23, 2016. The Siberian Husky Club of Britain is holding its annual sled dog rally over the weekend. (Photo by Russell Cheyne/Reuters)

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 White Crested Poland is seen at the National Poultry Show on November 20, 2016 in Telford, England. The annual event continues to grow with around 7000 entries this year from all around the world. (Photo by Leon Neal/Getty Images)