Your photography must be made by you and must be accompanied by a proof. It can be:
a second photography with a paper with "My entry for the SUNSET PHOTO CONTEST by @flamingirl" IN FRONT OF THE SUNSET. Not only a paper because it does not prove anything ^^:
the original version of your unedited photo
the photo of your camera with the image on the screen
you with your camera with the image on the screen
that is a lot of rules girl.
Do you have a better idea to avoid fraud and photo plagiarism?
no