I don't think many employers value a piece of paper that effectively says "someone purporting to be Conjou took an online course and passed". I'm sure there are some online diploma mills educational institutes like Atlantic Intercontinental University that will argue with that statement.
Unless a regionally or nationally accredited college is giving you credits, or a legitimate recognized professional organization (think AICPA, etc.) is verifying your achievement, there is little need to get a piece of paper that proves an online course was taken. The programming skills you claim to have learned will be verifiable quite clearly if you're ever asked to code something as a component of an interview or evaluation of a job opportunity.