There's a more basic question I realized I should ask, don't be insulted if you're way more advanced, because the simple things are where all troubleshooting should start.
Are you sure you're using completely uncompressed images? JPG images, even directly off your camera, are compressed, and this looks EXACTLY like image compression artifacts. In fact, since I am able to see the same problem on my screen as you see on your screen, then the problems is DEFINITELY in the image and not a problem with the display. (unless you actually took out your camera and took a picture of the screen.) Even if that really is a photograph of your screen, it still looks EXACTLY like image compression artifacts that you're seeing.