Remove light/dark lines

[nikopol]

   

First of all, sorry if I post in the wrong section and if for some the answer seems obvious.

I did some research but did not find the solution to my problem.
I want to remove light and dark vertical and horizontal stripes that appear on my image. 
These lines appear because the image is composed of 200 thumbnails stitch together. The areas of overlap and the difference in brightness and contrast of each tiles make these light and dark lines appear.
If you have a step by step solution (I am a beginner) I am greatly interested.
Thanks in advance