This isn’t just a gray patch, it’s a large number of dots. I hope you can see them.
If you can’t, try enlarging the picture on your screen.
Actually, I could only get a quarter of a million dots – 250,000 – into that photo. (And a speck of dust, which was originally too small to see, so that I didn’t brush it off.) So you’ll have to look a second time–
And a third time–
And a fourth time–
Now you’ve seen a million dots.
Now do all that twice over again, until you’ve studied the picture and counted the dots twelve times over, and then you’ll have seen what the number “three million” means.