That picture you posted on Instagram from the beach last week might have more useful data in it than you think.

Where are you? What do you have in your hand? Do you look happy or sad? What are you wearing? These are all questions that can help advertisers target their marketing to consumers, so a crop of new digital marketing companies has begun analyzing photos posted on Instagram, Flickr, Pinterest and other photo-sharing sites to look for these trends and insights.

Ditto Labs Inc. uses photo-scanning software to locate logos in these personal photos (is the subject wearing a North Face jacket? Or holding a can of Coca-Cola?) and look at the context in which these brands are being used.

For example, according to the Wall Street Journal, Kraft Food Groups Inc. pays Ditto Labs to find their logos on Instagram and Tumblr. Ditto Labs then analyzes trends like what people drink when they’re eating Kraft products and how happy they appear to be. They are then placed into categories like “foodie” and “sports fan” based on how they’re eating their Kraft food.

Digital marketing firms use personal photos in other ways, too; Piquora Inc. stores massive amounts of these images over a few months to look at trends over time.

This new brand of marketing research serves as a fresh reminder that the photos we put online are public, and once we click ‘post’ we lose control over who sees them and what they’re used for. “This is an area that could be ripe for commercial exploitation and predatory marketing,” Joni Lupovitz, vice president at children’s privacy advocacy group Common Sense Media, told the Journal. “Just because you happen to be in a certain place or captured an image, you might not understand that could be used to build a profile of you online.”

Write to Tessa Berenson at tessa.berenson@time.com.