OpenGL is very particular about threads.

So, it turns out that every thread that uses OpenGL needs its own rendering context.
Currently, the thread running in the ImageFactory class does not have one. Let's call that thread imageProducerThread.
This means that I must either:

Join the launch thread from imageProducerThread,
Create a new context on imageProducerThread,
Move all the OpenGL stuff to imageProducerThread,

All of these require lots of re-writing....
Sigh, I guess moving everything is the best solution.

Dang.