Every year the city photographers chase clues and take snaps of Cardiff in a one-day competition firstly introduced in the UK by the Welsh capital.
During the competition photographers have 12 hours to take 12 pictures after they receive the same number of clues. The different themes of the pictures will be revealed every four hours during the competition.
At the end of the day, each photographer memory card is collected and pictures printed out so that a panel of judges can see them. The winning pictures will be exhibited.
Photomarathon is an international event as it takes place in Denmark, Germany, Netherlands, the Czech Republic, France and Russia. It was firstly introduced in the UK eight years ago, in Cardiff 400 participants register to participate.