This effect is the simplest one to get an irregular edge with transparency. It is done by creating a transparent (alpha) layer for the whole image then erasing selectively. This effect can look good as an overlay on a wood background.
Create a transparent irregular border in GIMP using the Eraser Tool
- Open image.
- Select–select all.
- Layers–Transparency–Add alpha layer.
- Select the eraser tool. There are several shapes and texture types to choose from.
- Erase selectively with the tool the way you want the edge to look.
- Export your image as a .png file to save the transparency.