Suppose that a user have attached a
Jack.jpg file as a attachment to a online InfoPath 2007 form, is there a way to retrieve or extract the full URL of this attachment file
If I haven't misunderstood your situation, the attachment files are stored as blob data inside the xml of the form, so there's no permanent URL for the image.
I think it will be stored as a Base64 encoded string inside the XML file. I would suggest writing a custom .aspx page which takes a querystring parameter to identify the document that can retrieve the raw XML and convert the Base64 encoded attachment into binary and send it back to the browser.