Two problems with condition 6.
1. Where is the necessity? Bear in mind the links to ECHR and the need for necessity to encompass a "pressing social need". Also when you look at ICO guidance he emphasises need to consider other ways of meeting your objectives.
2. Strictly Condition 6 is just not available at all as photos are technically probably sensitive personal data as they show race / ethnicity. See Murray v Express Newspapers & Big Pictures (UK) Ltd  EWHC 1908 in which it decided that photographs are likely to constitute sensitive personal data.
Finally if you get around that you still have principle 2 purpose limitation to contend with.
Bottom line IMO you need consent.
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