Erica Jong states, ‘Erotica celebrates the erotic nature of the human creature…and does so artfully, dramatically. Pornography on the other hand, serves simply as an aid to masturbation, with no artistic pretension and no artistic value.’
I believe the difference between the two is greater however -- it's more than the quality of the lighting and the sets.
Both erotica and porn deal with sex and sexuality, both are designed to arouse their audience and titillate.
I believe that the key differences between erotica and porn are emotion and empathy
In erotica the writer (dealing with text as E2 is a text medium) exhibits respect for all their characters. There is a motivation for them to act as they do, and they are portrayed as living, feeling beings, with an existence above and beyond their sexuality. Even if all you see in the scene described is sex, you are aware of the characters being people. There is likely to be at least an intimation of a relationship between the characters.
In porn, one or more of the characters is liable to exist solely to fuck, to be fucked, or to be the subject of fantasies about fucking. There is no feeling of connection to, or respect for, this (these) character(s)
Any portrayal of rape in a titillating manner is pornography. The same is true of paedophillia, mind-control, and debasement of all kinds where one or more party in the narrative is treated without empathy. In a real-life situation these activities are not erotic, they are terrifying, and the victim will not respond with anything but fear. Describing any other response is a masturbatory fantasy.
BDSM is a special case -- it's a kink that I personally cannot understand, but I would argue that again, if the dominant partner is shown as having a genuine affection for the submissive partner, it is erotica, otherwise it is pornography.
In the same way, movies like the 'Emmanuelle' series, or girlie magazines are pornography, because they objectify and present characters/models as sex-driven automatons or pieces of flesh.
It is, of course also true that the quality of the writing, lighting, acting, and so on, is generally far higher in erotica than in pornography. I'd suggest that this is an extension of the concept of respect -- this time, to the audience.