im = rgb2gray( imread('Picture4.png') );
contour(im,4)
There is an obvious difference between specifying 2 (contour levels) or 3. However, you have to be looking fairly closely to tell the difference between 3 vs 4. You probably will not be able to tell the difference between 4 and 5.
The image appears to be consistent with the possibility that someone converted an image to black and white, and then write the image as jpeg, and then read in the jpeg and wrote it as png. That is, the values that are not 0 (black) or 255 (white) occur only in boundary positions as-if they only existed due to the way DCT handles sharp edges (it blurs them, like anti-aliasing.)
