Using Masks and Layers—Painting, Filling, and Color Tools - GIMP 2.6 for Photographers: Image Editing with Open Source Software - page 261

Now get ready to paste eastercard.png on the new image. You will be
virtually integrating it into the television.
• Use the Measure tool to measure the width and height of the gray
rectangle in pixels. Write down the two values.
• Return to the eastercard.png and select the Image > Scale Image menu
item. Scale the image so that its width will be roughly 100 px smaller than
the rectangle in monitor.xcf .
• In the monitor.xcf image, use guides to mark a border of about 50 px in
the gray rectangle. Export the main layer from the eastercard.png image
and align it along the marked border in the gray rectangle.
• You may need to scale the height of the gray rectangle. Select either
the Scale Tool or Layer > Scale Layers . Make sure the border beneath the
exported image is wider than the one above it.

• NOTE
You can select the unit of
measurement for the Measure tool
in the settings at the bottom of the
image window. For the purpose
of this exercise, you should select
pixels, px .

You can also position the front layer and the inserted eastercard copy layer
with the help of the Alignment tool (see also section 3.12.2). To do this, you
must crop the two layers to the size of the image by selecting the Layer >
Autocrop layer menu item.
Having done this, activate the front layer in the Layers dialog. Then select
the Alignment tool in the Toolbox. In the tool settings, choose Active layer from
the Relative to drop-down menu. Now select the image area of the Easter
card image in the image window. To do so, click into the window and create
a rectangle around the image object by holding the left mouse button. This
way, you tell GIMP what is to be aligned.
In the next step, click the Align center of target button in the tool settings
of the Alignment tool . The Easter card will be aligned in the center of the
horizontal center axis of the front layer.
Then set the value in Offset to 50 (pixels) and click the Distribute top edges
of targets under the Distribute button.
Since the two layers have been aligned with each other, they have also
been moved and positioned on the image area. Therefore, you can link the
images together in the Layers dialog. Simply click left of the preview image
next to the two layers. A chain icon appears. Now you can reposition the
linked layers with the Move tool .
What you need next are surroundings for the screen.
• Create a selection along the contour of the imported eastercard layer.
Since you don't want the program to find the front layer's image contour,
set the front layer to invisible in the Layers dialog. Make sure the Select
Transparent Areas and Sample Merged options for the Fuzzy Select tool are
selected. Click the Fuzzy Select tool on the transparent area around the
image object in the image window. Everything around the object has
been selected. Now use the Select > Invert function to precisely select the
object's contour.