Phase correlation with permissive license

I need to compute XY shifts between pairs of almost-identical images with deep sub-pixel accuracy within a Micro-Manager plugin. I don’t need to actually merge the images, just extract the shift.

I have been using the GDSC Align Images FFT method and it works quite well. I believe the phase correlation in BigStitcher is essentially the same thing. Both these have GPL license; IANAL but I think that means I can’t distribute my plugin code using either of these because Micro-Manager is more permissively licensed, which runs counter to my long-term goal of making my plugin part of the Micro-Manager distribution.

Does anyone know of similar code that has a less restrictive license? Or have other ideas for me? Thanks!

Edit: for those who may not know, Micro-Manager is a technically a plugin of ImageJ and is distributed with its own copy of ImageJ (but not FIJI). Thus it is trivial to access any “ImageJ-native” processing routines within Micro-Manager. For my development work I have copied a few JARs from GDSC into my Micro-Manager folder and can access methods from the JARs from my plugin code, but I don’t think those JAR could ever be distributed with Micro-Manager due to license conflicts.