There is not much information on providing a source when an image is sourced from Facebook. I recently uploaded an image, ID 4985301, and I believe it should be approved, but I am unsure if it will due to the source (and the approvers perhaps not knowing much about Facebook sources).
I made sure is a direct image link, as is mentioned below, on the wiki page for "Bad Facebook ID":
Example page link: https://www.facebook.com/Page_name/photos/ID_1/ID_2/.
Example direct image link: *.fbcdn.net/v/*/filename.jpg?_*.
It is recommended to use page links for sources, because direct image links are temporary.
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The wiki page for Facebook also needs updating, as the information is unclear:
"If you upload image/pictures that source is based on Facebook, You can input source by open the image tab and open the new tab of the image in another browser tab and copy the link."
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Lastly, I made sure the image I uploaded (again, ID 4985301), was not uploaded on the artist's Pixiv, Twitter, or DeviantArt accounts. The Facebook link is all there is from what I can gather.