The distinction between denotation and connotation can be made in textual analysis and the existence of dictionaries is used to support the argument that the sign system begins with a simple meaning that is then glossed as new usages are developed.
Louis Hjelmslev (1899-1965) therefore proposes that although the function of signification may be a single process, denotation is the first step, and connotation the second.
Roland Barthes (1915-1980) added a third possible step in world view or Weltanschauung in which metacognitive schema such as liberty, sexuality, autonomy, etc.
In the real world, a human observer has binocular vision, but the two-dimensional picture must be analysed to determine depth and the relative size of objects depicted by applying rules of perspective, the operation of which can be confused by focus and composition.
While it is true that an unedited photograph may be an index, digital technology is eroding the viewer's confidence that the image is an objective representation of reality.