Semiotics - Study of Signs
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Types of Signs [Charles Sanders Peirce]
Signify by  Resenblance  Causal relationship  Conventional or arbitrary relationship 
Process  Can recognize the object  Can figure out the relationship  Must learn the relationship 
Example  Photograph  Smoke and fire  Religious symbol 
Visual Example 
How We "Read" an Image
Definition  Structure of the image  Meaning of the image  Effect/impact of the image 
Example  When we took the two curves and put them together to make a simple abstract fish, we were doing syntax. The two curves are like a subject and verb that combine to make a sentence.  While each of us may see the same general image, we each have our own understanding of the image and thus our own meaning. Catfish does not mean the same to each of us.  When an image causes us to have a response, we are aware of its effect on us. Most of us view a swastika in a generally neutral manner, but had our relatives died in concentration camps, we might respond much differently. 
Some Additional Concepts
Method of Creating
Visual Example
Condensation - the process by which we combine elements from unrelated images to form a new image. In this example, the face of a person is combined with the image from a computer program to give a new image of a person with a unique way of seeing the world -- through the eyes of computer software. This image was part of an advertisement.  Face + computer software menu  Unification of unrelated elements 
Displacement - the process by which we transfer meaning from one sign or image to another. Displacement images often have strong sexual associations derived from Freudian psychotherapy. The Crown Royal ad given here needs little explanation in terms of its sexual meaning even though it was used as a Christmas ad suggesting Santa might want to visit this particular house.  Arrow = penis  Substitution of one element for another, often with sexual associations 
Metaphor - the process by which we gain understanding by means of an analogy. Here we see censorship compared to a book of matches whose cover is the U.S. flag. There is a clear analogy between the concept of censorship and flag burning.  Book as matchbook  Analogy of one known element to some concept or unknown element 
Metonymy - the process where we use an image to create an association in the mind of the viewer. In this case, the feeling of being on a lake with the one you love, or would like to love, is a positive analogy. The use of the orange to represent both the setting sun and the liquor adds to the impact of the association.  Sunset = romance  Association where one positive element is used to focus attention on a good feeling about the object or product.