I think I saw a mythbusters show that talked about ectoplasm. They recreated the pictures perfectly, making me feel like they were fake. But then again, any ghost or angel picture could be faked too. I've heard of people who could help an entity manifest or help them communicate. Honestly, it's just like any form of medium abilities. You could prove it to be fake, but it doesn't mean that it is.

Someone sees the future... call it De Ja Vou.
Someone sees a 'ghost'... call them paranoid
Someone talks to a spirit... call them crazy.
Someone has a dream that really happens... They read too much into them.
Someone has creepy smoke come out of their mouths and a ghost appears... well, they're faking. lol

I have no proof on the truth of Physical Meduimship, but I don't have proof of the nonexistance either.