./WordTracker.sh http://<someurl>/img.jpg
This will add http://<someurl>/img.jpg to the footer of the Tracker.docx file, creating Tracker-armed.docx. You can open Tracker-armed.docx and add whatever other content you want. Now just monitor your server for IPs accessing the img.jpg
Use a 1x1 white pixel. This can be generated on the command line with:
echo iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mP8Xw8AAoMBgDTD2qgAAAAASUVORK5CYII= | base64 --decode > pix.png
Also, it's probably best to use a unique filename, so bots/crawlers don't stumble across the image.