A woman was sexually assaulted onboard a train service from Blackpool to Liverpool, say police.
Officers are investigating the assault which took place on the journey from Blackpool North to Liverpool Lime Street on Saturday, August 21.
Shortly after 11.30pm, a man boarded the service at Wigan, sat next to the woman and began talking to her.
He then exposed himself and sexually assaulted her before he was asked to move to another seat by the train conductor.
But the man soon returned to the seat where he continued to harass his frightened victim, before leaving the train at Edge Hill station.
After reviewing CCTV footage, officers want to speak to the man in the image provided as part of their investigation.
If you know who he is, you should contact British Transport Police by sending a text to 61016 or calling 0800 40 50 40, quoting reference 2100060257.
Alternative, you can call Crimestoppers anonymously on 0800 555 111.