They deployed something like this in Buenos Aires a few months ago (or maybe a year?). It worked mostly in Subway stations, where there is a lot of people every day passing by.

Although it catched a few fugitives - it triggered a lot of horror stories. A lot of false positives - which in an ideal world wouldn't be that bad. A police man would stop you, asking you a few questions and once he confirms you are not the guy they are looking for, they would leave you free. But it wasn't like this - even when the police man recognized you weren't the one looking for, they have to take you with them to the comisary, and spend a few hours here until a judge can set you free. Worst of all, there are a few stories of people being false recognized on a Sunday afternoon, and had to spend in the comisary until Monday when the Judge could go. Very very sad.