This simple service calculates a sha256 hash of any file you select, and allows you to copy/paste it into your Steem post for a basic kind of copy protection. It allows you to prove using the Steem blockchain that you had access to the file on the date you posted it.
Proving you had the file at a specific date/time requires both the SHA256 hash being in the blockchain, and that you still have a copy of the exact file that you hashed. If you change your file at all, the hash will not stay the same. So you should probably keep a backup.
I don't know whether this method would constitute legal evidence, so unless you have more knowledge please don't assume so.
If you use Linux on your PC, you can do exactly the same thing using the command:
If you hash the same file, you will get the same hash as you get using this tool.
I have been using this until today, but this tool makes it easier for most people. I'm certain there will also be tools for Windows and Mac PCs, but I haven't investigated them.