My passport's Machine Readable Zone is damaged. How do I deal with it?

If the machine readable section of your passport is damaged, as it is in this photo, your passport must be replaced. A passport scanner cannot read this. If your passport is a newer e-passport with the chip embedded, this damage also makes the chip unusable. In both cases, the airline and immigration will not accept the document for travel.

You can renew your passport now, but you can only use the online portal to do so if it has less than 7 months to expiry. Otherwise you will need to apply via a Regional Passport Office in Pakistan, or your nearest high commission or consulate if you are outside Pakistan.

This passport is not just damaged, it has been tampered with!

You should under no circumstances have fixed the digits with ink yourself. That blue is clearly an attempt to make the numbers legible again.

This passport is no longer fit for use, and the only option is to replace it.

Be prepared to be questioned when you go to renew this passport, even if the fix was made in all honesty, it is not taken lightly. You can possibly be fined for it as well.

Forget the airline or whether someone will accept it or not. If you go to an airport in Pakistan with this passport you might possibly be arrested and asked to explain the fix.

Thanks to a comment by @uberqe, here is some relevant information from The Passport Act, 1974

6. Penalties for certain offences relating to passport.- (1) A person shall be punishable with imprisonment which may extend to three years, or with fine, or with both, if he:-

...

(d) forges, alters or tampers with any passport or any document which he uses for obtaining a passport; or

(e) uses a passport which has been forged, altered or tampered with; or

...

Nowhere does the law say that if the alteration is done with a good motive it would be fine. I am not a lawyer but in my opinion, a hand made alteration to fix the passport number or any relevant ID information is a significant alteration. When the passport was water damaged, it was just damaged and that wasn't a big deal. When more ink was put on it, it was altered.

I would never use this passport, except for a renewal.

The scanners that are used in airports regarding passport control scan (sliding) the passport through the passport control gadget that they have, which in this case is impossible due to the damage on the critical points of your passport, so in the case it will alarm the officer that the passport is damaged. Of course the officer may input the numbers manually; however I'm not sure if someone will let this slide, so I recommend that you get a new passport.