Ask HN: What malicious things can someone do with a copy of your passport?

In a currently popular HN article about someone getting all of their stuff stolen[1], they mention that a person likely got hold of copies of their passport. I have also had concerns about someone potentially getting their hands on one of the many copies of my passport I have floating around. Should I be concerned though? What malicious things could a person potentially do with the information on a passport (US or otherwise)?<p>[1] http:&#x2F;&#x2F;levels.io&#x2F;100-to-0-things&#x2F;