How can you verify if this american visa is legit and not fake...

Africa? Would that be Ghana? Is someone asking you for money?

You can assume it is fake, if they are sending you a copy trying to Prove it is real.

Tell us how they are trying to con you out of money,
Is it a dating scheme?
Perhaps a gold transport scheme?

Get a copy of the visa page, and contact US consulate where the visa was issued.

If this is from Ghana, then you and jump to a conclusion, it's fake!!