A stranger bashed a 25-year-old woman in the head with a baseball bat in an apparently unprovoked attack in Chelsea this month, cops said as they released the first images of the brute. The victim was walking on Seventh Avenue near West 23rd Street around 10 p.m. Feb. 8 when the menace suddenly struck her with the weapon, authorities said. The senseless assault left herwith a cut and bruising, and she was taken to Lenox Hill Hospital, where she was listed in stable condition, police said.