This isn’t really a fully developed thought, but how about an autoencoder of some kind? You would want it to accept the two halves of the image as input and reconstruct the full image.

Edit: yeah, seems like that rough approach has been used in this work:

https://www.semanticscholar.org/paper/StitchNet%3A-Image-Stitching-using-Autoencoders-and/d67cd5a13f7671fe56262265c2439a0d75cb89c0