ABC News' Reena Nina reports:
The yo-yo diet. Grapefruit diet. Cabbage diet. Roni Noone had tried them all. In the end, she lost 70 pounds the old-fashioned way, through diet and exercise.
Noone posted a photo of herself on her website every month to document the year-long transformation, and said she was shocked when she discovered her photos were being used to promote diet products.
"I started a blog and kind of committed to journaling my thoughts and feelings regardless if I was gaining or losing," Noone said.
One ad, which erroneously said that her name was Jess, claims her weight loss happened in 30 days.
Noone told "Good Morning America" it was "scary" that someone could use her picture in a way "without even one grain of truth" to sell a product.
Internet experts say this isn't an isolated case. Even Kate Middleton's images were used without her consent to plug diet products.
"It's not just the princesses of the world or the famous celebrities of the world," said Hemanshu Nigam, chief executive of SSP Blue, an online safety consulting firm. "You're going to find that people are doing this to common folks like ourselves."
Nigam counsels clients on how to protect themselves online. His advice? Use watermarks on any photos you post, placing them high enough so they can't be cropped out.
For anyone thinking of using those photos, those watermarks will make it hard.
"If it's more trouble, they're not going to want to spend time," Nigam said.
Noone has had difficulty tracking down the companies that used her image. ABC News found a mailing address for one of them, but that address turned out to be a post office box in Pompano Beach, Fla.
Noone described the companies as "this nameless faceless thing you can't go after."
She has written cease-and-desist letters to email addresses she's managed to find, all to no avail. When the images are taken down, they surface again in as little as 24 hours.
In order to drown out the negative ads, she's asking people to post her real weight-loss story, and she's reminding everyone about the reality of her journey.
"It's not possible to sell weight loss in a bottle; it doesn't exist," she said. "I got happy, then I got skinny."