From government whip Jay Hill:
Last week, on behalf of Justice Minister Rob Nicholson, I introduced Bill C-31. This legislation [...] proposes to streamline the identification process in police stations, allowing the fingerprinting and photographing of persons in “lawful” custody who have not yet been charged or convicted of specific offences.
Read that one again. You haven't been charged. Maybe you never are. Yet the police have your prints and mugshot.
The relevant text is here.
PS. This piece from the Niagara Falls Review claims that:
According to the Conservatives, the change would only apply to serious crimes like murder, kidnapping and sexual assault.
Well, specifically, they apply to any "indictable" offence. Not that it makes a difference.