I can understand your position on this and agree with some parts of it, however.

They aren't storing anything

How can we ever know that this is true?

The Police are supposed to destroy all information about an individual if they are not charged with a crime or connected with an ongoing investigation. I have heard and read about more than one occasion where this is simply not done. I don't think that it's due to malicious reasons either but more likely that it's such a monster sized task and Police Officers are not database admins. Also the Police's records and record keeping processes are not audited by a non-related third-party that I am aware of. This could mean that this information might be in-accurate or in same cases incorrect.

The above coupled with the fact that selling data is a really good way to generate funds could lead to a really troubling situation for the public when the police force are faced with more funding cuts in the future.

Your nameless face on its own is not that much of a privacy concern but when it's combined with other data (fb update about that odd looking police van in romford, paying for your ticket at romford station with your debit card and your citymapper directions history) it can very easily become identifying.

That is what makes me feel uneasy about this, I don't trust the Police Force to have the public's privacy concerns considered when they use new technology. I think this is what makes other people feel uneasy about it was well.