British Transport Police are investigating an incident which occurred on board a ScotRail service last month.
Detectives have now released a CCTV image of a man who may have information on the incident.
The incident occurred around 11:45 pm on the 18th April between Glasgow Queen Street and Camelon.
The man has been described as being in his early 30s, slim built and wearing a cream jacket.
Should anyone have any information, they should contact BTP via 61016 or by calling 0800 40 50 40, quoting the reference 23 of 19 April.
As always, anonymous reports can be made via Crimestoppers on 0800 555 111.
Responses