A default thumbnail representation is created when you build
a widget using any of the widget configuration wizards.
For Google Gadget widgets , the thumbnail graphic is derived from the image
posted in the gadget directory. For example if you go to http://www.google.com/ig/directory?synd=open
and select a gadget, such as "Clock and date", click "View
source" and note the following variable/value in the XML to see where
the gadget's thumbnail graphic is defined:
For Web Page and Feeds widgets, we use "favicon.ico" from the
website, just like the browser does.
For any widget you create, you can edit the "imageUrl" variable
in the widget's extension file (extension.xml) to specify whatever thumbnail
graphic you want using a local file or HTTP URL.
The graphic you specify for the catalog document has no effect on the widget
thumbnail used in the My Widgets sidebar panel.