(CNN) A young girl poses provocatively in a dark hotel room. For a set fee, any willing customer can pay to have sex with her.

For investigators attempting to track down sex traffickers and their victims, these online advertisements can contain critical clues.

The smallest of details in a room could give away its location, but there are too many ads for law enforcement to scan each of them for clues.

That’s where TraffickCam comes in. It’s a simple phone app that uses crowdsourced snapshots of hotel rooms to help law enforcement locate victims and prosecute sex traffickers.

Any travelers pit stopping at a hotel can turn on their phone’s GPS location and upload photos of the room from four different angles to TraffickCam’s database.

The idea is that law enforcement agencies can then check adverts featuring suspected trafficking victims in hotel rooms against TraffickCam’s database of photos.

TraffickCam’s image analysis tools transform the photos into a number of data points, using features such as patterns on the carpet, paintings on the wall and landmarks out of the window. The various data points in the photos play an important role in matching the location.

TraffickCam is the brainchild of Exchange Initiative and a team of researchers at Washington University. Congregation of the Sisters of St. Joseph provided a $100,000 matching grant to begin development of the app, and private donations are made through the non-profit St. Louis Community Foundation.

“This is an easy way for citizens to take a stand against sex trafficking by simply taking photos,” Kimberly Ritter, director for development for Exchange Initiative, tells CNN.

Since launching in June 2016, Ritter says that more than 150,000 hotels have been added to the TraffickCam database.