>>2190810There are plenty of tutorials on-line. And GIMP itself comes with a good 'help' function.
I opened one of the images in GIMP
Created a new layer, selected a rectangular area on that layers, and filled it with black.
You can tell that's the current layer because the thumbnail (lower right) is outlined. The opacity of the layer is 100.
I dragged the opacity slider down until I had the look I wanted.
At this point, I captured my screen, closed the image, and then opened the screenshot so I could add a (badly-drawn) arrow pointing to the layer-opacity control.
I'm still learning GIMP myself since the software I used to use was crippled by Windows 10. I checked out a GIMP book from the library.
