Labour has held Batley and Spen in the by-election caused by the killing of MP Jo Cox
Detective Constable Lee Thimm, of Leeds District CID, said: "The suspect was among a group of men socialising at the pub. It has been suggested they could have been from the Wakefield, Castleford or Pontefract area.
"I would like to hear from anyone who recognises the man or who has any information that could assist the investigation.
Anyone with any information is asked to contact DC Thimm at Elland Road via 101 or call the independent crime-fighting charity Crimestoppers anonymously on 0800 555 111."