Can someone explain the scam where girls from Ghana send letters and photos looking to start a relationship?

Here is the Question: Can someone explain the scam where girls from Ghana send letters and photos looking to start a relationship?
I have received multiple letters and photos from attractive young women in Ghana looking to begin a relationship and describing their attributes. I have not responded, but am curious about the source of this scam and how i can get off the list.

Best found answer:

Know better? Leave your own answer in the comments!