بسم الله الرحمن الرحيم
The girl and boy should appoint someone wakil for their nikah and when the wakil will solemnize the nikah in the presence of two witnesses then it will be valid. The nikah is valid in both the cases whether the boy or girl watched each other through internet or not.
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.