Police would like to speak to him as a potential witness following an assault in Lancaster last month.
It was reported to police that at 4am on Sunday April 1 a man was assaulted on Cheapside.
The victim – a man in his 20s – was punched twice to the face and suffered a broken jaw.
He was taken to the Royal Infirmary Infirmary for treatment and later discharged.
DC Nikki Marshall of Lancaster Police said: “This has been a nasty attack which has resulted in the victim suffering serious injuries.
“We believe the man wearing the white shirt could hold vital information to our investigation and we’d like to speak to him.
“If you know him, or think you could be the man in the pictures, please contact us.”
Anyone with information is asked to email police on firstname.lastname@example.org or call 101 quoting crime reference WB1803517.