You will need OpenCV, Festival installed for this to work:
sudo apt-get install python-opencv festival
The text files named hi and bye are the files from which Festival speaks when a face is detected (hi) and when the face leaves the screen (bye). You can modify these files as necesary to get the desired speaking for each face event. Be aware that using pi-blaster for the servos means you can't use the analog audio anymore - it's busy generating the PWM signals for the servos. Audio must be via HDMI for this to work. This is a setback for now, sorry.
I used the OpenCV code on this webpage: http://www.technolabsz.com/2013/03/how-to-easily-install-opencv-on.html
Included is the Python script and the human face XML from which the OpenCV uses to identify the faces. I modified the facedetect.py script to work with the servos and festival output - this is the script that you have now from this Github repo.
run using
./execute.sh
or
./facedetect.py --cascade=face.xml 0