Mystery locations around a city centre provide a puzzling poser for people who receive a civic calendar for next year.

Images of Durham 2002 features 13 close-up shots of buildings in and around the historic core of the city.

Unlike previous years, there are no captions accompanying the 12 monthly scenes and the front cover photograph.

Instead, recipients of the calendar are challenged to identify all 13 locations and return their answers on a competition entry slip provided on the back cover.

Entries need to be submitted by the end of January. The first three containing all 13 correct answers will win a signed, framed print by calendar photographer Royston Thomas.

The next ten will receive signed copies of his Images of Durham book, which contains a foreword by the Chancellor of Durham University - actor, writer and raconteur Sir Peter Ustinov.

Durham City Council commissioned Mr Thomas, of Nevilles Cross, to provide photographs for the calendar for the tenth year. It follows the success of previous publications, which have carried his distinctive interpretations of familiar city landmarks.

Copies of the calendar are traditionally sent around the world, many providing stocking fillers for Durham exiles at Christmas.

The council ordered a print run of 3,000 copies of the calendar this year and expects all to be snapped up from local book stores and from the city's Tourist Information Centre.

John Jennings, city council director of environmental services, said: "It needs Royston's remarkable visual eye to capture the unique charm of Durham, year after year, in timeless, stunning images."

Mr Jennings added that his work helped to reflect "what sets Durham apart form other cities," in selling it to overseas companies.

Mr Thomas said he decided on the competition theme after seeing drinkers in one of Durham's most famous hostelries puzzling over locations in past year's calendars.

Speaking at the launch, at the Half Moon Inn, in New Elvet, he said: "I've had more than the occasional drink here, and I've overheard many an argument over where the pictures are taken. Everyone likes a quiz, so I put the idea to the council and they agreed."

Mr Thomas took 30 shots around the city and the best 13 were selected for the calendar, which is available for £5.