How to Make a Fading GIF in Gimp
Instructions
1Open the image that you want to use on your computer.
2
Start GIMP. Select "Open." In the dialog, locate and open the image you loaded.
3
Right-click on the background layer in the "Layers" panel, and choose "Duplicate." Repeat this four more times.
4
Select the second layer from the bottom, and reduce the "Opacity" to 80 percent. Reduce the next layer to 60 percent. Continue this process until the top layer is reduced to 0 percent.
5
Select File" from the menu, and choose "Save As." In the dialog, choose "GIF" as the file type, and click "Save."
6
Click "Save as Animation" in the next dialog, and click "Export." In the next dialog, choose the "Delay" between frames and change the "Disposal" to "Replace." Click "Save."
Source...