Okay, open SketchUp and Go to Window > Styles. Next, click on the icon with the "ok" on it, which is the Watermark Settings icon. Then, click on the + sign. Find that image you want, then click "Open". Then choose from either "Background" or "Overlay". Both the same tutorial steps, you can change the transparency of the image with the model. Next choose "Stretched", "Tiled", or "Positioned". Click "Finish" when you're done. PRESTO! Example:
Or with "Overlay".
If you want to share your model with your background image, please upload it here!
poster-Invader ZIM

