Prostitution Part 3

While watching Taboo, I pondered about something.  What is the difference between pornography and prostitution?  Obviously, one is legal and the other is mostly illegal, but why?  Prostitution involves one party, usually the male, to pay the other party a certain amount of funds in order to receive sexual favors or other erotic stimulation.  In pornography, both parties, or all parties involved, are paid to preform sexual acts upon each other.  Are the only differences who's getting paid and who's purchasing, or is there something more to it?  Pornography is made to be recorded and distributed.  Prostitution on the other hand is not, but there are cases where it was recorded for ones own personal pleasure.  It seems to me that there really isn't a truly distinguishable characteristic between the two, and that both should either be legal or illegal.  Any argument against prostitution can be used against pornography.  Is the decision literally just a proverbial line in the sand based on some sort of social moral or stigma, or is there more to it?