A woman withdrew cash from a machine in Carolgate, Retford at around 4.45pm on Friday November 5, but forgot to take the money.
The next person to use the machine took her money and did not hand it in.
Officers have now released images of a man they would like speak to who may be able to help with their enquiries into the incident.
Police Community Support Officer Emma Porter, from Nottinghamshire Police, said: "As part of our ongoing enquiries we've released this image of a man we'd like to speak to who we believe may be able to help our investigation.
"I would urge anyone who recognises him or who has any further information to please come forward.”
Anyone with any information should call Nottinghamshire Police on 101, quoting incident number 665 of November 9, or Crimestoppers anonymously on 0800 555 111.