I meet a man on line. He scanned his passport. How do I verify it?

You can't since you don't have access to that database. If a man you met online needs to prove something by scanning his passport for you then there's a problem somewhere.

Contact the consulate office in US and request for verification. Some don't provide this service... but it doesn't hurt to ask.

Don't trust anyone you meet online especially people from countries in Africa. Don't send money and don't try to get them here.. if you want to meet him/her, you go there.