In reply to Will_Thomas_Harris:
I've seen the need for receipts referred to in many insurance policies. That is the first step to check with your policy. If it's there you are on a weak starting point, but could still take the matter to the ombudsman if you feel it is unfair, hidden, badly worded, etc.
I understand that the point is photos don't prove ownership and apparently some folk claim for items they never owned. On the other hand, neither does some receipts, but if your in possession of the receipt, then it's more likely.
With your photos, are they date stamped? Are you in the photo? Do you have multiple photos of same items over time? Do you have records of items for PPE records? If you could should same item over a period of time, particularly with you/your records then it helps to show some continuity of probable ownership.
If you bought items online or large shop (relatively) recently, lots of companies keep computer records of purchases (linked to loyalty cards or similar etc) and so you could approach them for evidence of purchase.