A source told Britain's Daily Mirror newspaper: "Victoria loves Marc's work but she wasn't entirely comfortable with getting naked.
"Marc went all-out to persuade her. And when she heard about what a great cause it was she knew she just couldn't turn it down. The picture she and Marc have chosen is amazing - sexy but tasteful."
Victoria - who has three children, Brooklyn, eight, Romeo, five, and two-year-old Cruz - will follow in the footsteps of Julianne Moore, Dita Von Teese and Naomi Campbell, who all stripped for Jacobs' T-shirts in 2006.
They raised £30,000 for the charity and it is hoped Victoria's raunchy effort will match that figure.
Meanwhile, Victoria is said to be worried about her looks as the Spice Girls embark on their world tour.
She is reportedly terrified she looks the oldest out of all of the girls - Geri Halliwell, Mel B, Emma Bunton and Mel C - and is very insecure.
A source said: "Victoria has the biggest insecurities. She is worried about her skin, which is very bad again, and her hair which is falling out.
"She feels she has aged. When she saw the pictures from the press conference they did in the summer, she was upset because she thought she looked the oldest out of all of them."
The tour starts on Sunday (02 Dec 2007) in Vancouver, Canada.
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