thats the only thing I don't see done the same way on http://www.shadowbox-js.com/usage.html
also i think your images have to haev the rel='shadowbox" attribute so you could check for that as well
alos did you chec k the net tab in firebug to make sure it's fetching the image images/Sympathy-card.jpg ? maybe it should be /images ?
also content: looks to be literal content, so maybe
should be :
'<img src="images/Sympathy-card.jpg" />'