Its a Canival FFS, not a Police Identity Parade. Leave People be.
"as well as individuals wanted by police who it is believed may attend Carnival to commit offences"
I'm assuming that wording was written and approved by kill joy Theresa May.
Sounds like an extension of Theresa May's 'go home vans'.
If you have overstayed your Student Visa//Visa/Work Permit or an illegal immigrant (given the ethnic diversity attending this event, concentrated in this area), you're committing an offence? Sound like as much.
To translate technically for you - That's pretty much a Cart Blanche open ended, Data Slurp, to test Facial Data against the whole of the UK Passport Database (to also see you is attending this event, and from where).
We'll find out later 'post-Canival processing' - its a trial system linked up to all the faces stored on UK Passport Database, to check for illegal immigrants, to give Theresa May some bonus points by Brexiteers.
What not clear is this a data slurp with 'live' processing of 'select individauls', or will also be a retained mass data slurp for post-Carnival processing through Hadoop data crunching systems against Interpol/UK's Passport Database.
It really amounts to passive-aggressive supression by the Police that has a domestic violence type whiff/attitude about it, to keep people in check.
Better idea: Turn off your Cameras, and enjoy the weekend, it achieves nothing but resentment. Leave people be, its a carnival, not an Police Identity Parade.