Filling the blue area with white (you can do this in Paint, it's not difficult) reveals the first part of a secret URL.
The second part is hidden in the source code for the "blue box" page, at the very bottom.
Putting the two together leads to a page where all the existing Sandra and Woo strips are archived as ZIP files, along with an offer for a free upgrade to the next tier of giving if you support Sandra and Woo on Patreon.
At the bottom of this
page is a note with the name "Boris Floricic", a deceased hacker and phone phreaker who went by the handle "Tron" ( https://en.wikipedia.org/wiki/Tron_(hacker)
). His specialty was voice cryptography, and I tried converting the image file into a sound file, but had no luck, so unless someone else comes up with something, that's where the trail ends.