Publishing good photos only will only lead to people getting wrong impressions.
People will see all the good stamps in photos, join, and get a garbage lot. And if they can't publish a photo of the stuff they got because it was bad, they'll likely leave.
On the other hand, publishing bad photos, will draw people's attention to what is not acceptable in such exchanges. If the fault is not particularly well visible in a photo, marking it with a circle (or otherwise) is also something I support.