You are very right Oreofe.
When I first joined Upwork, I had that fear because of the international image of the country but I didn't spend up to a week after my profile was approved before I started getting jobs, and they have been coming ever since.
I get jobs from clients across the globe. Within a space of four months I had worked with clients from America, Asia, Middle East, and of course Africa. I have also worked for a Nigerian who lives in Canada. and on my profile, it is boldly displayed that I am from Nigeria. So, I vehemently disagree that Nigeria's international image play a significant part in determining your job opportunities on Upwork. I think the principal determinant is your competence. Clients want their jobs done excellently, if you do your job so well, they will come back for you next time.
Rather, I think where the challenge lies is in payment. receiving money is quite difficult. Since, I cannot receive money into my paypal account and withdraw into Nigerian bank account, I have to always part with $30 per wiretransfer after paying 10% or 20% on each job. The charges are simply excruciating. I haven't found an alternative or a resolution yet.