I think screenshots illustrating the "problem" might be helpful. If I zoom in on a photo and the area is darker than that area would definitely be darker on the screen. So apparently you are seeing a problem different from what I am understanding. Please illustrate so that we can understand the problem.
On the other hand, if you have a GPU and have it activated that could be the source of the problem. You should try turning off GPU acceleration and see if that solves the problem. If it does then you could check to see if there is an update to the driver for your graphics card.