The image on the front and the big image on the back has had the same effect added to them. It's just a "Linear Light" Blending Option. The result of the effect is quite different from image to image, it depends on factor like, the size of the image, the amount of details, the colors etc.
I just tried changing the blending option on the other images, and it looks a little funky.
My covers may only be viewed on well calibrated screens and printed on well calibrated printers.