Praise be to Allah, the Lord of the World; and blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
A videocassette alone would never be considered legal evidence to prove something or to carry out the Hudood set by Islamic Shariah. However, it might be a legal presumption taken into consideration by a judge to find out the truth and to make a larger inquiry in a case based upon the accompanying circumstances in which the cassette was recorded.
The evidences to charge one with guilt are only three according to Islamic Shariah. They are testimony of witnesses, confession, and taking an oath.
A judge of Islamic Shariah is not allowed to carry out the legal punishment (Hudood) without having the legal evidence to prove guilt of the accused.
However, it is liable for a judge in an Islamic court to punish a person just to discourage further criminal behavior when there are indications of his criminality, if it is useful.
If one commits a crime and he undergoes punishment for that crime then it is not permissible for anyone to punish him again for the same crime. But if he repeats the crime then he should be punished again.
Allah knows best.