My first line of 'defence' against such an approach would be to politely ask if they are familiar with the Police and Criminal Evidence Act 1984 Code B relating to seizure of property and ask to see their card outlining their powers as a PCSO. Their seizure powers are limited to tobacco and alcohol from minors, vehicles used to cause alarm and distress (joyriders), and to the seizure of prohibited articles found during a search when accompanied by a police constable.

If they wish to do a stop and search of a pedestrian under the Terrorism Act 2000 or later amendments, it can only be done in the presence of a police constable and a PCSO can only detain you for up to 30 minutes to establish your identity (or wait for a PC to arrive) if you have committed an offence. As far as I can see in PACE, there is absolutely no mention of the taking of a photograph in a public place as being an offence.