The star rating on the leaderboard is a way for users to know if they have been uploading and transcribing quality images. The ratings reflect how others see your uploads. When an image is uploaded and sent to transcription the image receives a rating. The rating on the transcription page is done by clicking on the red flag in the transcription process. ***  See the Article: How can I rate an image while transcribing? 

From the BillionGraves Website:

#1 Click Leaderboard

If you have one or two stars do not worry! Go to My Stats and look through the reasons your images were rated poorly. You can clean them up by clicking on the reasons listed, re-transcribing them, and earn back your shiny five star rating!

Where the leaderboard page is. 

Your star rating. 

My Statistics Page. This can also be found at: