Idea: Highlighting new parts in a step

[Travis Cobbs]

No, he merged the two images. For this to work, both need to be the same size (in pixels), and also both have the same camera settings. Then, drawing the second image over the top of the first yields the merged image. If you look at the second image in an alpha-aware image program, you'll see that everything except the lines is fully transparent (alpha value of 0).