didjvu software package provides DjVu encoder with foreground/background separation, 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 didjvu
didjvu is installed in your system.
Make ensure the didjvu package were installed using the commands given below,
$ sudo dpkg-query -l | grep didjvu *
You will get with didjvu package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Graphics |
| Package | didjvu |
| Version | 0.8-2 |
| Description | DjVu encoder with foreground/background separation |
| Sub Section | Graphics |