Mayor Michael R. Bloomberg in the same way that soda companies and big tobacco are. But they are, in a sense, the impetus for City Hall’s latest public health campaign.

Mr. Bloomberg is taking on the popular, unattainable notions of beauty promoted by professional image-makers with a campaign that tells girls that they are beautiful the way they are.

Mainly through bus and subway ads, the campaign aims to reach girls from about 7 to 12 years old, who are at risk of negative body images that can lead to eating disorders, drinking, acting out sexually, suicide and bullying. But unlike Mr. Bloomberg’s ads to combat teenage pregnancy, smoking and soda-drinking, which are often ugly, revolting or sad, these ads are uniformly upbeat and positive.

“I’m a girl. I’m funny, playful, daring, strong, curious, smart, brave, healthy, friendly and caring,” one ad, featuring DeVoray Wigfall, a robust, laughing 12-year-old from University Heights in the Bronx, says. The ads show girls of different races and sizes, some playing sports and one in a wheelchair. Each one ends with the campaign’s overall slogan: “I’m beautiful the way I am.”