Estimate gap between two adjacent images
There are multiple papers dealing with this issue, using similar methods (extrapolation beyond the image edges to create a virtual overlap).

Alignment and Mosaicing of Non-Overlapping Images by Yair Poleg &amp; Shmuel Peleg

Building a Mosaic from Non-Overlapping Images by Benjamin Choi

A Novel Technique for Non-overlapping Image
Mosaicing based on Pyramid Method by Achala Pandey &amp; Umesh C. Pati