SlaughteredMelon said:
Make sure to provide a source when uploading this image, and to parent both posts; read the Post Relationships manual.
Also, reminder that uploading third-party edits and paid rewards is against the Upload Rules, so make sure to check twice your sources before posting.
If the uploader was given the image directly, because they commissioned it, then they don't need a source because they are the source. They also don't need to worry about it being a paid reward, because as far as we're concerned the commissioner is the owner of the image and can use it how they want, including uploading it to Danbooru, even if the artist also uploaded it to their own sites as a paid reward.
It really just depends on why this person has the image. If they received it as a paid reward, then they shouldn't upload it. If they commissioned it, then it's fair game.