That is really simple...
Suppose that the default image has this path:
imagewin:/C:/Documents and Settings/Master/Desktop/logo_aci.jpg
Now all you need to do is set the auto-enter option*** of the container field to be calculated with this calc:
Self & ¶ & "imagewin:/C:/Documents and Settings/Master/Desktop/logo_aci.jpg"
If the container will be cleared, it will display the default image.
*** Remember to clear the box: Do not replace existing value for field ( if any )