How to change grey level for overlapping images?

I would like to make not so visible the border between two overlapping images. How to make the gray levels of the images that overlap as similar as possible, linearly transforming the gray levels? How to do it taking only the means and standard deviations of the pixels that overlap between the two?

Thank you very much in advance for your answer.

Answer 1

[Image Analyst]

See this example from the Computer Vision System Toolbox where they stitch the Mathworks global headquarters building together from separate photos: http://www.mathworks.com/help/vision/examples/feature-based-panoramic-image-stitching.html?prodcode=VP&language=en

[Auryn_]

Thank you, but unfortunately it doesn't work with the grey levels of the images superposition...