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In the worlds of fashion, beauty and advertising, models are routinely tweaked and trimmed in photos. But critics of the practice say it promotes unrealistic ideas about body image. So CVS, the nation's largest drugstore chain, announced Monday that it will stop "materially" retouching models in ads for its store-brand beauty products by 2020.

"The connection between the propagation of unrealistic body images and negative health effects, especially in girls and young women, has been established," Helena Foulkes, president of CVS Pharmacy, said in a statement.

To bring some transparency to its marketing, this year CVS will add a watermark — what it's calling a Beauty Mark — to images that haven't been significantly retouched.

CVS defines significant alterations as changing "a person's shape, size, proportion, skin or eye color, wrinkles or any other individual characteristics." The company plans to issue a set of guidelines for what it deems acceptable airbrushing.

CVS aims to push its suppliers in a similar direction. Those that don't comply with the new standards will get slapped with a "digitally modified" message by 2020.

With more than 9,700 stores, CVS holds a degree of sway in the industry. Among the company's suppliers are Procter & Gamble, Johnson & Johnson, Unilever, L'Oreal and Maybelline.

The beauty aisle should represent the "authenticity and diversity of the communities we serve," Foulkes said.