Comment by dr_dshiv

There's a video that's quite convincing: https://youtu.be/K0Xio5yo_x8

It inverts the second image and passes the first and third images under it, and when there is a complete overlap the combined images make a nearly perfectly gray rectangle, showing that they cancel out.

Look at the "scratch" on the right end of the leftmost dash. That "noise" shouldn't be replicated, right?

Try looking at the artifacts, not the actual bands. There's a little black hairline on the top right corner of the leftmost band, and a similar line toward the left of the middle band.

The page has another comment with an animation where they're overlaying the images to show how similar (same?) they are.

The linked video makes it pretty clear by subtracting one image from the other and showing the difference: https://www.youtube.com/watch?v=K0Xio5yo_x8

Ironically there was a whole post about basically exactly this the other day: https://news.ycombinator.com/item?id=42655870

Any image manipulation program like photoshop with layers, you put the suspect images on top of one another and use filters to subtract one layer from the other (I'm not sure which filter operation works best, it might be multiply or divide) and then work to align the two layers. Differences and similarities become extremely obvious.

You can also get the raw pixel information by converting to a bitmap and comparing values, but it's easier visually because it's pretty trivial for a simple image modification to change all of the pixel values but still have the same image.