In advertising these days, the brass ring goes to those who can measure everything  how many people see a particular advertisement, when they see it, who they are. All of that is easy on the Internet, and getting easier in television and print.

Billboards are a different story. For the most part, they are still a relic of old-world media, and the best guesses about viewership numbers come from foot traffic counts or highway reports, neither of which guarantees that the people passing by were really looking at the billboard, or that they were the ones sought out.

Now, some entrepreneurs have introduced technology to solve that problem. They are equipping billboards with tiny cameras that gather details about passers-by  their gender, approximate age and how long they looked at the billboard. These details are transmitted to a central database.

Behind the technology are small start-ups that say they are not storing actual images of the passers-by, so privacy should not be a concern. The cameras, they say, use software to determine that a person is standing in front of a billboard, then analyze facial features (like cheekbone height and the distance between the nose and the chin) to judge the person’s gender and age. So far the companies are not using race as a parameter, but they say that they can and will soon.