PCSO's have no such powers, and police do not except in specific circumstances. But you may save yourself from being arrested if you comply.

• Police do not have to have any reason to make a stop and search under the Terrorism Act , so you are faced with the interesting task of proving a negative, that you are not a terrorist. Showing them your photos may make it clear that you are innocent. However stop and search is sometimes being used as a means to discourage all  photography, in which case the preciise nature of your photos is irrelevant.
• If police want to see a photograph because they believe it may assist investigation into a criminal matter, they have a right to collect evidence. If you do not comply you may be arrested for obstructing a police officer, withholding evidence or even conspiracy to pervert the course of justice, depending on circumstances. As noted, professional newsgatherers have some protection from this in PACE.