facedetect software package provides simple face detector for batch processing, you can install in your Debian 9 (Stretch) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install facedetect
facedetect is installed in your system.
Make ensure the facedetect package were installed using the commands given below,
$ sudo dpkg-query -l | grep facedetect *
You will get with facedetect package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Graphics |
| Package | facedetect |
| Version | 0.0.+20150428-1 |
| Description | simple face detector for batch processing |
| Sub Section | Graphics |