Semiotics studies the communication, between signs and what they mean.
Denotations is what the picture contains and the connotations is what they mean and what we connect to them.
We see thousands of images every day, and we always read them, inactively or actively. The object of image analysis os to understand the meaning of a work of art/design.
Sign, signifier and signified – The sign is the whole that results from the association of the signifier with the signified. “A sign is anything that makes meaning” – Saussure
“A sign is anything that can be used to tell a lie” – Umberto Eco