An Asian security guard at Tesco Express in Blackpool Road, Preston, was racially abused by a shopper he told to leave, police said.
The worker became the target of the woman's expletive-filled rant after stepping in as she argued with store staff, at around 10.40pm on Wednesday, July 19, the force said.
Officers investigating the hate crime today released a picture, taken from the shop's CCTV footage, of a woman they want to speak to.
PC Janette Cahill, from Preston Police, said: "We need to find the person responsible.
“Following enquiries, we would be keen to speak to this woman.
“If you recognise her, please contact police immediately.”
Anyone with information can contact police on 101, quoting crime reference SA1711656.