Detection of pixels in image that are not in focus

I am trying to process a set of images to identify certain color ranges of pixels. The problem that I am running into is that some of the pixels of the image is not in focus (Please see the image below).

Is there a way to identify the areas of the image that are "blurred"? For example the bottom right part of the image is not in focus, I want the program to identify this area as not in focus and change the color to black.

Answer 1

[Walter Roberson]

"blur" is perceived when there is a loss of detail -- corresponding to loss of high frequency information.

If you do a low pass filter on the image, and subtract from the image, then the areas that have little change are areas that have little high frequency content (and so might be blurry)