A 77-year-old woman was bitten by a dog as she walked past a community centre on Sunday, February 24.
The incident happened in Spencer Parade, Stanwick, at about 10.30am.
A Northamptonshire Police spokesman said: “She walked past a man with a black dog on a lead. The man was talking to a runner who was stretching next to a car with a woman sitting in it.
“As the lady walked passed the man, the dog lurched at the woman and bit her arm causing minor injuries.
“The man is described as white, in his sixties, wearing a trilby type hat with a black rim. The runner was wearing a high-visibility jacket.
“Officers are keen to speak with any witnesses to this incident, in particular the runner and the woman in the car.” Anyone with information should call Northamptonshire Police on 101.
Information can also be given anonymously to Crimestoppers on 0800 555 111.