Using Masks and Layers—Painting, Filling, and Color Tools - GIMP 2.6 for Photographers: Image Editing with Open Source Software - page 233

• Choose View > Zoom > Fit Image in Window ; adjust it so you can see the
entire image in the working window. Make the rulers visible ( View > Show
Rulers ). Pull guides from the rulers and position them at the same distance
from each side, thus marking a frame with equal width to all sides of the
image. The dimensional information provided by the rulers will help you
measure the border accurately.
• Use the Rectangle Select tool to draw a rectangular selection over the
guides. Use the Select > Invert menu item to invert this selection. This
selects the frame area to be filled.
• Create a new layer called frame in the Layers dialog.
• Choose the Patterns dialog from the dock window or open it by choosing
Windows > Dockable Dialogs > Patterns . Select a filling in the Patterns
window that appears. Note that the patterns appear smaller as image
resolution increases.
• Select the Edit > Fill with Pattern menu item. The selected area is filled.
• Remove the selection ( Select > None ).
• You can repeat the steps you followed when you created the single-color
frame if you wish to bevel this frame or add a drop shadow. Don't forget
to save your image.
Figure 3.55
The Patterns window with the prepared fillings and frame