[web2py] Linking to uploaded files (when using separate folders)

[Yarin]

I have an image table, modified from the image_blog example, like
this:

db.define_table('image',
   Field('title', unique=True),
   Field('file', 'upload',
   uploadfolder=os.path.join(request.folder,'static/userpics'),
   uploadseparate=True)
)

I want to be able to generate a static link to the image, but have no
way of knowing which folder the image has been inserted into. How
would you do this?