A provocative work of conceptual art by Yoko Ono, John Lennon's widow, has been branded "offensive" by the half-sister of the former Beatle.

The controversial work, entitled My Mummy Was Beautiful, features images of a woman's breast and crotch. The posters, which are dedicated to Lennon's mother, are on display on buildings across Liverpool as part of the Biennial art festival in the city.

Julia Baird, Lennon's half-sister, has complained the work is disrespectful to her mother, who died in a car crash aged 44.

Ono said it was initially about her own mother, but chose to dedicate it to Lennon's when it was decided to display it in the ex-Beatle's home town. "I remembered how John loved his mother, and it choked me up," she said.

Mrs Baird has urged the festival organisers to remove the posters, which are displayed on a church and a nearby street popular with shoppers. The posters that have caused most offence to Mrs Baird are displayed at St Luke's Church, which is soon to be inaugurated as a peace centre. The centre wanted to mark the event by displaying works by Ono, a prominent peace activist.

But, Mrs Baird said: "I find it totally offensive that you can use images of a breast and a vagina displayed all over the city, and then make the implied link with my mother. I have nothing against Yoko Ono as she was simply commissioned to do the work. The same images are on display at the Tate Gallery (in Liverpool's Albert Dock) and I don't have a problem with that, but the others I find upsetting and I would like to see them removed."

As one of the most original performance and installation artists of the 1960s, Ono is also viewed as one of the founders of conceptual art. Her ability to shock came to the fore in her film Bottoms, which showed the naked bottoms of people walking, while last year she was stripped to her underwear on a Paris stage by members of the audience as part her show Cut Piece.

Lewis Biggs, Liverpool Biennial chief executive, said Ono's work had been requested by St Luke's Church, which had made her one of its patrons, and would remain in place until the end of the festival on 28 November.

"I had no intention of offending anybody," said Mr Biggs, "but equally it has been very well received by some people who have found it has provoked thoughts of their relationships with their own mothers."