When is a Text not a Text?

We've been discussing 'Text' again in class, as part of 'Text Technologies: A History'. So, we pondered when is a Text not a Text? When it's anything except words, which are always 'text'. But we'll only allow words as long as the words are definable as such--as words. That is, they cannot be random markings or even structured-but-uninterpreted markings, since markings that have no discernible meaning cannot be 'text', because they don't mean anything and 'text' must have meaning. (One should surely argue here that meaning is not a one-way street; I can produce text with meaning to me, even if no one else has a clue what I'm talking about. And besides, meaning is always subjective.) Or, ok, not 'words' per se, but symbols; symbols constitute 'text'. Such a definition permits us to include ideographs or pictographs as 'text', except these are, to all intents and purposes, images, and we don't want to allow images as 'text'. Or do we? If something can be read, if something is open to interpretation in a social act of communicative intent, then presumably it is text, even if that thing being read has nothing verbal in it or around it; it is simply a photograph or picture.