A local radio station wrote a check on a man's t-shirt, and the guy went into the bank, pulled the t-shirt off his back (all the while on a cell phone calling in the details), and cashed the check. You do NOT need special paper or magnetic ink or anything else. All you need is a way to print them so they look ok. As long as the Route number and your checking account number are on them, the bank will accept them.
That does not mean the power company, water company or mortgage company will...you may have to fight them if you sent in a T-shirt...but a printed check should not be a problem anywhere.
I print my checks on regular paper off of my regular printer and pay my bills with them.