Clubbers in San Francisco are staying away from bars using a new app that scans faces of patrons and reveal their age and genders.

The app, SceneTap, provides real-time updates on the crowd-size, average age and male-to-female mix ratio to users so they can decide if it is to their liking.

The app's relies on biometrics to identify genders and age, said The Herald Sun. A camera at the door takes the patron's picture and the software will map features to a grid. By measuring distances between features such as eyes, nose, and ears, then matching the results with a database of averages, it can guess the patron's age and gender.

App makers say they do not identify individuals or save personal information and, so, do not infringe on patron's privacy rights.

However civil rights experts say facial recognition technology has advanced to the point that having your picture taken potentially offers the same information as giving someone your fingerprints.

Computer programs can break down high resolution images with detail to identify distinctive features on individual faces. Those patterns, not so much the image themselves, can expose individuals to people who do not even know them. In theory, the program could match the photo to identifiable online images such as those found on Facebook, said a staff attorney with free-rights advocate Electronic Frontier Foundation Lee Tien.