Add a form variable to the form:
- File, Form Properties
- Click "Variables" tab
- Click + button
- Enter a variable name (i.e. BackgroundVisibility)
- Set value to "hidden" (without the quotes)
Add background to Master Page:
- Click "Master Page" tab above form (nevt to "Design View Tab)
- If "Master Page" Tab isn't visible, Right click on the gray area to the right of the tabs, and make suer "Master Pages" is checked off in the contect menu that appears.
- Insert an Image Field and resize to the area that you want the background image to fill
- Note* Make sure you use an image field, not an image. Image fields let you use scripts, images don't.
- Format the image field as desired (i.e. remove caption, add border, etc.)
- Select the image to use for the background, by setting the URL field in the image object properties.