I just found this solution and it helped me, and then I found a nice way to show your "noimage.jpg". You make a report function which sets a persistent variable containing the path to your image (I use the Request scope, so "Request.imagePath" for example). The variable is set to your "noimage.jpg" if it can't find the image path. You can pass parameters to the function from your query, if you wish. The function itself always returns "true". Call this function in the "Print when" property (remember, it's always true so it will always show), and the persistent variable is used as the image path. That way you can have your proper image or your default image show.
I almost gave up on the CF Report Builder -- the report functions made it cool enough to keep using.