Let’s say that you’re a brand, like Nabisco or the North Face, and you want to see what people are saying about you online. You could do a text search of Facebook and Twitter, but that’s soooo 2009, and you can’t guarantee that people will always label the photos they take. Instead, third-party companies are slurping up every public photo that you upload online and scanning them to see what you’re eating, drinking, and wearing.

So Starbucks knows that there’s a picture of me holding one of their cups and smiling that I posted to Instagram. So what? People who are savvy about the Internet and about privacy simply assume that any picture they post online can be used for any purpose. Not everyone is that savvy, though, and even people who are that savvy probably don’t suspect that their photos are being scanned and analyzed to find smiles, trends, and “influencers.” This week, the Wall Street Journal broke down how this works and how your photos might be repurposed.

When you agree to the terms of service for a social media site, you might be agreeing to third-party use of your photos, but you may not have thought that sites like Tumblr were selling “firehose” access, or a blast of every picture posted on the site to be scanned for facial expressions and brand logos. Well, they are, to Ditto, a company that helps companies analyze how they “look” online.

Here’s what the Ditto Labs “firehose” looks like. Anyone can watch it in real time, not just clients.

How can you protect yourself from being part of such a marketing effort? Well, you can’t, unless you refuse to post photos online that are accessible to the public, and also forbid friends, co-workers, and event photographers from doing so as well. You could never take a picture of a brand logo, or blur them all out of your photos before uploading.

Smile! Marketing Firms Are Mining Your Selfies [Wall Street Journal]