Some dude who streams video games and, apparently, is a pro-SNP and Scottish Independence guy.

I’m assuming you’re using Gimp:

1. Open your image

2. Duplicate the original onto a new layer and hide the original (it’s just… always a good idea)

3. Right click the new one and choose “add layer mask.” This has a bunch of options that don’t matter, choose white (full opacity).

4. There’ll be a new image thumbnail in your layer, next to the main one. This is your mask. You can click on the thumbnail to draw to it. It’s like another layer.

5. Wherever your mask is white, your image will have full opacity. Wherever your mask is black, your image will be transparent. Where the mask is gray, it’ll be translucent. Don’t fool around with non-grayscale mask colors, they’re usually a bad idea even if you know what you’re doing.

6. Using the brush tool, draw black onto the mask where you want to hide the image. You can use multiple strokes, it’s just an image. If you mess up, you can undo, or you can draw white onto the mask. Being able to go back and forth between erasing and redrawing with the brush is why masking is so much better.

7. You can toggle the original layer’s visibility back on to see what it looked like, which helps when figuring out how you’re tracing a low-light thing. Like I said, it’s always a good idea.

8. The “x” key shortcut (swap foreground background colors) is very handy for this stuff. The little black and white box that sets the foreground/background colors to black and white is probably designed for this.

I made some, including this Rosa image.