How to merge parts of an image aligned to their edges?

[felixcra]

Consider the following image as an example:


https://i.imgur.com/E91iXwL.png



What is the best way to merge the upper and the lower part together?

Edit: It might be better visible what I need if you have a look at the imgur image instead of the embedded image here, as there you can clearly see the borders of the parts I want to merge.