Using Masks and Layers—Painting, Filling, and Color Tools - GIMP 2.6 for Photographers: Image Editing with Open Source Software - page 232

3.8.2 Creating a Frame with Pattern
The basic steps for creating a frame with a pattern are almost identical to
those previously described. The only difference is that you'll need to create a
selection for your frame.
The Procedure
Follow these steps to create a frame with a pattern:
• Open the girl-color.png image from the SampleImages folder on the DVD.
• Choose Image > Canvas Size to increase the width or height of the canvas
to the desired size. Press Enter . Since the chain icon is closed, each side
will be increased proportionately. Click the Center button; then click
Resize to enlarge the canvas.
• Add an alpha channel (using the right-click menu in the Layers dialog)
to the background layer of your image. Add a new layer underneath the
existing one in the image and colorize it white or with any other desired
color.
Figure 3.54
The image with guides and selection before inverting the selection