have you tried to extract the vignetting pattern form the captures and using it to normalize them? My first try would be to calculate the median grayscale image of all 9000 captures and then using this to normalize the intensity.
That said, a full BRDF is not the only way to approach this problem, especially at reduced resolution where the artifacts are more apparent.
If you're an ACM member, there is a wealth of information in SIGGRAPH publications. Having been in graphics since the 90s, I started with Foley and Van Dam (Computer Graphics: Principles and Practice) and Watt and Watt (Animation and Rendering Techniques) and then stayed on top of SIGRAPH (attending regularly, though not annually) since then.
For a more whimsical survey from the pen of a straight up genius, Jim Blinn's books (e.g. Dirty Pixels) are fantastic reads.