1) Convert NEF to JPG using online link above, and download to your computer
2) Open JPG in Windows Paint
3) Select a box of the yellow black image immediately above the "2400" text approxiamately twice as high vertically as the "2400" text is, and about 50% longer horizontally.
4) "Copy" the rectangular selection.
5) "Paste" the selection
6) Drag the pasted the selection to the same place you copied it from, so it overlaps the original and then
7) Select the lower edge of the pasted selection and pull the lower edge downward until it is almost to the bottom of the yellow box. Too low and you will see it against the black frame of the concrete thing, and too high and you will see the horizontal line between the "2400" and the bottom of the yellow area.
The copied image stretches leaving a smooth graduation from top to bottom, matches the colors perfectly at the top line and hides the differences at the bottom because it is close to the bottom of the yellow box. So the only place that might not look good are the two sides, which in this case, they did.
I make memes and have been practicing these types of techniques for a couple of months. Took me more time to download the NEF file than it did to do the work. Hope you are happy with it.