Image analysis -calibration

[MM_24]

Hello, I'm trying to match the two x-ray images. They differ from each other due to the radiation course shown in the figure. The pixels in the second image are more stretched at the edges and there are fewer changes in the center. The object in these pictures in the center does not change much and is stretched more and more at the edges. These changes only apply to one way x axis. The changes between these images appear rather like a function (IMAGE BELOW). I have absolutely no idea how to fit these two pictures together so that they can be superimposed for later analysis. I will be grateful for any help, I apologize if the question is very trivial, but I am just starting my adventure with image analysis.