Correcting fisheye distortion and stitching images in quadrant

Hi! I’m a marine biologist and have little experience with ImageJ/FIJI. I’m mapping shrimp burrows using a Gopro camera, this results in pictures with bare sediment and shrimp holes (indicated with red arrows). For each map, I have taken four pictures, I would like to stitch these pictures together in a quadrant, after correcting the fisheye distortion.

A

B

C

D

I have attached an example of the kind of images I want to stitch together, they are arranged in this order:

C / B
----/-----
D / A

The only part of the images that I’m interested in is the surface within the quadrant.
Sincere regards,
Tom

Recently there was a discussion about that kind of distortion, see:

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