The background of a scanned image (the part without anything drawn) is white and needs to be transparent.

To do this, please see the following steps for each kind of image.

For line art

If you scan your line art, you can use the Convert Brightness to Transparency function in the Edit menu to easily turn the white areas transparent.

1. Select the scanned line art layer.

2. Select Edit menu > Convert Brightness to Transparency.

Any white areas will become transparent and show as a checkerboard pattern.

For colored images

If you have scanned a colored image, you can use one of the following methods to give it a transparent background.

Select the Eraser tool and erase the white areas around the colored image.

With the Fill tool selected, select transparency as the drawing color, and fill in the white areas with the transparent color.