Well the traceback is showing that the Python script is failing when importing the ImageFont class from the Python Image Library (PIL), it seems something isn't installed in the expected location on the system when you're running this as root and returning an IO error.
Looking at the github repos where you got the adafruit library (which is deprecated btw) and the monitor script there is a setup.py script that you would run as root, did you mistakenly run the setup as pi instead of root? You could always start again and revisit the setup/installation process as root.
Personally if it works OK as the pi user in a shell try running it as the pi user in rc.local, e.g.
... you can see the above includes a redirect for stdout & stderr to the file /tmp/monitor.log which you can inspect for messages/errors.
If this works in a shell but still doesn't from rc.local maybe rc.local is too early in the system startup process for you to be trying to run this script.
Looking at the github repos where you got the adafruit library (which is deprecated btw) and the monitor script there is a setup.py script that you would run as root, did you mistakenly run the setup as pi instead of root? You could always start again and revisit the setup/installation process as root.
Personally if it works OK as the pi user in a shell try running it as the pi user in rc.local, e.g.
Code:
/bin/su - pi -c "cd /home/pi/Adafruit_Python_SSD1306/raspberry-oled-monitor && /usr/bin/python ./monitor.py >>/tmp/monitor.log 2>&1 &"... you can see the above includes a redirect for stdout & stderr to the file /tmp/monitor.log which you can inspect for messages/errors.
If this works in a shell but still doesn't from rc.local maybe rc.local is too early in the system startup process for you to be trying to run this script.
