'Add a picture
It uses the same convention as OOo, in that it saves the picture in
the zipfile in the subdirectory \'Pictures\'. The content variable
is a string that contains the binary image data. The mediatype
indicates the image format.'

def addPictureFromString(self, content, mediatype):

    ext = mimetypes.guess_extension(mediatype)
    manifestfn = ('Pictures/%0.0f%s' % ((time.time() * 10000000000), ext))
    self.Pictures[manifestfn] = (IS_IMAGE, content, mediatype)
    return manifestfn
