ikdind said:
Since the blacklist is applied client-side, would this mean that, technically, any post page would deliver the client a blank page and rely on javascript to reveal the image? Otherwise, could a person sent to a blacklisted post see the content before the blacklist was applied?

The option to block blacklisted post images could be made opt-in. JavaScript is already needed to make the blacklist work in the first place. All you lose is the ability to see an image loading, but you could have a click to reveal override.