The incident happened at the Asda supermarket on Ovangle Road on 1 December, say police.
According to police, a person requested £20 cashback at a self-service till, left the money by accident in the till and returned to find the money missing.
On a post to their Facebook page Morecambe police say: "We are looking to identify the women in this picture. We need to speak to her regarding a theft at the Asda on Ovangle Road. If you know who this is, then give us a call on 01524 596 986 or call '101' and quote crime number WB1609895."