I don't think the cost of the wedding pictures has anything to do with it, that was a service they paid for in NZ presumably(so nothing to do with HMRC) and would have cost more like a grand.
I mean if this USB stick got lost then the photographer could just send another, its value is simply the value of the stick itself - they've already paid for the rights to have copies of the photographs.
edit - OK they didn't even pay for them to be taken... so almost certainly OP has been overcharged for VAT