The Observer's 20 photographs of the week

The knight and his steed: using its suction discs for a firm grip, a red-eyed tree frog clings to a hercules beetle. The image, shot by Nicolas Reusens, is one of the entries for the 2014 Sony world photography awards. Entries are open until 6 January at www.worldphoto.org.
Nicolas Reusens says: 'Although controlled, this shot was not prepared at all, I was performing a workshop with the Agalychnis callidryas treefrog from Costa Rica when the frog managed to jump to the branch where this huge titan was sleeping … I had my gear ready so I only had to change a few settings and shoot … the rest is history' Photograph: Nicolas Reusens

Afghan schoolchildren take lessons in an open classroom at a refugee camp on the outskirts of Jalalabad, Nangarhar province Photograph: Noorullah Shirzada/AFP/Getty Images

A rare total cloud inversion is pictured at Mather Point on the south rim of Grand Canyon national park in Arizona. Cloud inversions are formed through the interaction of warm and cold air masses Photograph: Erin Whittaker/Reuters

Gillian Anderson posed, along with other stars, to raise awareness of the adverse effects of deep sea trawling, which is causing a collapse in the world's fish population.
You can see a gallery of Fishlove 2013 images here Photograph: Denis Rouvre/Fishlove

Maria Antonia Navarro Vargas changes the nappy of her daughter Esmeralda, as her son Juan Ramon, five, plays in the shack where they live in Madrid. Maria Antonia's family belongs to one of 13 Spanish Gypsy families who are at risk of having their homes demolished by orders of Madrid's town hall. The families, whose members are mostly unemployed, have lived in shacks they built themselves in a small settlement in northern Madrid for more than 10 years. They say they have not been offered any housing alternatives by Madrid's authorities and that the city's town planning board wants to evict them to make way for future plans to build a road on the land they occupy. The demolition of their homes has been held off so far due to the efforts of the Mortgage Victims' Platform Photograph: Susana Vera/Reuters

US first lady Michelle Obama reacts as two-year-old Ashtyn Gardner from Mobile, Alabama, trips over another child's walker after meeting Obama's new dog Sunny at the unveiling of the decorations at the White House in Washington Photograph: Jason Reed/Reuters

A scene outside a grocery store in a poor neighbourhood on the outskirts of Islamabad, Pakistan Photograph: Muhammed Muheisen/AP

Cookery writer Nigella Lawson arrives at Isleworth crown court in Isleworth. Italian sisters Francesca and Elisabetta Grillo, who worked as assistants to Lawson and her former husband, the art collector Charles Saatchi, are accused of defrauding them of over £300,000 Photograph: Peter Macdiarmid/Getty Images

A team of 63 daredevils break the record for the largest vertical skydive by women, in Eloy, Arizona Photograph: Norman Kent/Barcroft Media

An anti-government protester throws a bottle of water at Thai riot police as they attempt to remove barricades outside Government House in Bangkok Photograph: Dylan Martinez/Reuters

A girl poses for pictures, beside a burnt out police truck, with her boyfriend as anti-government protesters call off demonstrations outside Government House in Bangkok, Thailand Photograph: Dylan Martinez/Reuters

Grey seals play underwater by the Farne islands off the Northumberland coast, near Seahouses, northern England Photograph: Nigel Roddis/Reuters

An ultra-orthodox Jewish man lights candles on the sixth night of the Jewish holiday of Hanukkah, in a religious neighbourhood of Jerusalem Photograph: Menahem Kahana/AFP/Getty Images

An image of late South African president Nelson Mandela is projected on to the facade of Paris town hall Photograph: Charles Platiau/Reuters

A woman outside the house of former president Nelson Mandela in Houghton, Johannesburg, after news of his death emerged Photograph: Siphiwe Sibeko/Reuters

A poster depicting former South African president Nelson Mandela hangs on barbed wire as a Palestinian protester flees teargas fired by Israeli soldiers during clashes at a weekly demonstration against Jewish settlements at Bilin, near Ramallah, in the West Bank Photograph: Mohamad Torokman/Reuters

A Syrian boy cries as he looks for his mother while other newly-arrived Syrian refugees board a Jordanian military vehicle after crossing into the country at Ruweishid Photograph: Mohammad Hannon/AP

A severely wounded man lies in a Bangui mosque in the Central African Republic, following a day-long gun battle between mainly Muslim Seleka soldiers and Christian militias Photograph: Jerome Delay/AP

People walk on the North Sea beach near the town of Norddeich, Germany, in strong winds Photograph: Ina Fassbender/Reuters

Fernando Canini, director of Rome's wax museum, puts the the final touches to the new wax statue of Pope Francis Photograph: Gabriel Bouys/AFP/Getty Images