Using GIMP: Correcting and Touching Up Your Images - GIMP 2.6 for Photographers: Image Editing with Open Source Software - page 147

If you want to remove small blemishes such as dust from your scanned
slides, you can apply various filters. Have a look at section 2.8.2.
Figure 2.69
The image after the touchup
2.7.5 The Healing Tool
The Healing Tool is a relative to the Clone Tool . It's similar in how it's handled
and its settings, but it is for repairing minor blemishes.
Using the same steps you used for the Clone Tool, you can select a
section that corresponds in color and structure with the area you want to
repair. The difference is that the Healing Tool takes the surrounding structure
and brightness of the spot to repair into account. When you're covering up a
section of the image, the surrounding information has influence on the action
and its result. Small defects in a uniform surface are easily covered up. The tool
also works with larger surfaces; however, there is a risk that the characteristics
of the blemished section are more likely to remain. A large bright spot would
stay bright even if you paint over it with dark picture information. One
countermeasure is to use a brush pointer that is slightly larger than the spot
to heal.
Using the Healing Tool is a simple and fast way to correct your image. Try
it out and remove some wrinkles in a portrait.