Other mistake: The skull they used for the little girl in the well is obviously an adult's skull.
Other mistake: When Samara is falling down the well and we see the approaching water surface from her POV, there is a reflection of Anna looking down the well but no reflection of Samara.
Chosen answer: Samara broke her finger nail clawing at the walls of the well... I guess that's why it's on the tape also.
Paul Plesser