Defendants claiming that video is fake will be a challenge that future courts (and probably very near future, if not already) will have to deal with. In the short term, it will likely require the folks involved in the CCTV system to keep better records to show a proper chain of evidence, and be available to testify in court as to this chain of evidence. Courts have always had to deal with the veracity of evidence brought before them.

But it is a lot easier to have folks who are in charge of systems testify as to their authenticity than to have a child who has been abused testify to the authenticity of the abuse, thus the logic is defensibly limited to child abuse.