"The only caution we have is that sometimes what starts off as a really good idea starts being used for other areas which could affect privacy, begin stopping free speech etcetera," Kumar said. "At the moment it's going really well but without checks and balances there would be an opportunity for abuse of these systems."

Kumar added that "it wasn't very clear" in the announcement if the PhotoDNA technology would be linked to the existing online child exploitation filter which was "an area we have had concerns with."

"The ministry seems to be sitting on the fence in that regard," Kumar said.