•Legal definition of "Indecent exposure":
Main Entry: in·de·cent exposure
Function: noun
: the exposing of one's private body parts (as the genitals) either recklessly or intentionally and under circumstances likely to cause offense or affront
NOTE: Indecent exposure is generally classified as a misdemeanor.
Source: Merriam-Webster Dictionary of Law, © 1996 Merriam-Webster, Inc.
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You are right. Exhibitionism is different in a major way. It's obvious why it (indecent exposure) is illegal in any form, whereas pornography is illegal only if it is determined to be obscene.
Here's a "sub"-question to that: Say, a person is downloading his email, and it contains spam which displays an obscene photo meant to lure you to a pornographic website. Would that be similar to indecent exposure?
Is indecent exposure substantially different than obscene pornography?