Using Masks and Layers—Painting, Filling, and Color Tools - GIMP 2.6 for Photographers: Image Editing with Open Source Software - page 217

Here is an overview of the most important steps of this exercise:
• Open the images bluesky.xcf and hazysky.jpg from the SampleImages
folder on the DVD.
• Position the two image windows so that they partly overlap, arranging
the Layers dialog on the side.
• Click on the hazysky.jpg image to make it the active window. Click the
Background layer in the Layers dialog and drag it partly over the visible
bluesky.xcf image while holding down the left mouse button. Upon
releasing the mouse button, the layer will be pasted into the bluesky.xcf
image. This process copies layers rather than moving them.
• Rename the Background layer as hazysky . Move hazysky in the Layers
dialog so that it is positioned beneath the landscape layer. (The easiest
way is by dragging and dropping, or you can use the arrow keys at the
bottom of the Layers palette. Remember that the layer must be active if
you are going to move it.)
Finally, you must scale the layer so that it fits into the image. To scale the
layer, choose Tools > Transform Tools > Scale or just use the Scale tool from the
Toolbox and follow the steps described in the next section.
Figure 3.42
Copied layer with dashed border