Make a Grayscale Image Transparent with GIMP
- Open the image.
- In the Layers Panel, click Add Alpha Channel.
- If there are multiple layers, merge them together
- Convert it to greyscale (Image -> Mode -> Grayscale)
- Select-All & Copy
- Left click the Layers Panel. Yes, click it.
- In the Layers Panel, right click Layers pane and click “Add Layer Mask”
- Select the White radio button, then click Add
- Paste your image
- Invert it (Colors-> Invert)
- Click the Floating Selection and select New From Visible.
- Delete the Floating Layer and background images.