IT only costs 35 dollars to register a copyright.
The "poor mans" copyright only proves the date the ENVELOPE was mailed, not its contents.
Today, I will mail an empty 8X10 envelope to myself. When it arrives I will put it on a shelf.
In two years, I will go and watch a movie, and go home and write up a script based on what I saw. I will then seal it in the envelope and say I mailed it to myself.
This is why it won't hold up in a US court, if there is a good attorney present.
I am not an attorney, but I am married to an attorney who specializes in Intellectual Property
