Protecting works for being able to prove later “I've done this on this date”

If you want proof that you had item "A" at time "B" then your best bet is simply to hire a local lawyer. You send them your copyrighted material and they take receipt of it and keep it in a safe location. This covers off a number of points:

• Whomever you are using to prove your copyright needs to be impartial. Family and friends don't count.
• You'll want whomever keeps your copyrighted material to ensure that it doesn't get lost, burnt, etc. Good lawyers who deal with this kind of thing will have this in place.

There are also online providers for this kind of thing. UKCS provides this kind of service and I am sure there are other national providers.

If you want it done properly you'll need to pay out cash for this.

On the flip side, if you do find that someone is using your copyrighted material then, before you engage with them, get their documents/web-site/whatever notorised by a solicitor/lawyer. This will provide independent evidence that you were having your copyright infringed in the event that they then change their documents/web-site/whatever in order to avoid further action.

Finally: mailing stuff to yourself is basically worthless. If you want it done properly involve a lawyer.

Edit:

You don't need to do this in every country for which you want to enforce copyright. The reason you use a lawyer is to have someone impartial who will verify your copyright claim and provide evidence to substantiate it. Obviously, you want to choose a lawyer from countries with strong legal systems (US, UK, Canada, etc) as these will hold more weight than countries where corruption is more of an issue (Nigeria, etc).

Almost all major countries have Copyright Act. Contact local consultancies, lawyers etc. to know how to use it. Googling can also help.

There's no other more reliable way than legally copyright your work.

When it comes to GitHub type services, there's no guarantee that it'll survive by 2022 or not. Plus, an attack on their servers can screw things up silently.

Patents are the only CERTAIN way to protect your intellectual property work. (And also Utility Models of course.) If you cannot apply for a patent you can think of taking some compensatory actions to prove that you have actually created that work such as putting it on a well-known place, notarizing some of documents, finding some witnesses etc. But all of these methods are not guaranteed and can be objected at the court.

I assume you want to protect some kind of software, because that you are talking about GitHub. You cannot patent software, you can only patent it's alghoritm in many countries (if not all).

You had better finely document the alghoritm of your code and apply for patent. Of course, if you want to be protected in all countries, you will likely to apply for several countries and pay several fees, even though there are some liaison agreements between countries.

If you live in the USA then this solution is cheap and pretty solid.

You can print out your work / copy it and send it to yourself in the mail. Once you receive the letter, don't open it until you need it! Ideally you should print out another copy to keep with the letter (ie: paper clip the two together or keep them together in a file.) Please note: the copy that is not mailed is just for self reference incase you forget what is inside it.

All letters/packages sent via the US postal service* are stamped with a date as well as which post office the letter was processed at. Since the US postal service is a federal organization, it carries a lot of weight in court. Just make sure to seal the letter up nicely and keep it in a safe place until you need it.

*all letters and packages that I've seen from the US postal service anyway