A picture of the jump jockey Katie Walsh, looking mud-spattered, sweaty and tired, has won the photographer Spencer Murphy one of Britain's leading portrait prizes.

Murphy was named winner of the 2013 Taylor Wessing photographic portrait prize for a picture of Walsh that was taken at an advertising shoot for Channel 4’s The Original Extreme Sport Campaign.

Walsh, photographed in the colours of Seabass, the horse on which she came third in the 2012 Grand National, is the daughter of Irish trainer Ted Walsh and younger sister of jockey Ruby Walsh.

Sandy Nairne, the National Portrait Gallery’s director, who chaired the judging panel, said the image successfully conveyed everything that “jockeys go through and live through. It felt very powerful.”

Murphy, a London-based photographer, was taking pictures of a series of jump jockeys at Kempton for the marketing campaign. He has said previously: “I was keen to include Katie. I wanted to show both the femininity and the toughness of spirit she requires to compete against the best riders in one of the most demanding disciplines in horse racing. I chose to shoot the series on a large format film, to give the images a depth and timelessness that I think would have been hard to achieve on a digital camera.”

Murphy wins £12,000.