It need be no more complex than http://en.wikipedia.org/wiki/Special:Preferences#mw-prefsection-watchlist
In my opinion, it will need to be far simpler than that if it is to address the needs of the casual reader. We simply can't expect them to make any significant investment in understanding the process, unlike a casual editor who can be expected to make that investment. It needs to "just work". Primarily this is "just" an issue of interface design but that has not been a historical strong point for us ;)
Subject to gaming, well it's bound to be. But vulnerable to gaming, hopefully not. Fans of penises are welcome to add their preferences. That's why I didn't include the option "Hide all images except those that a fellow filterer has whitelisted".
Well, to be fair, you did initially include that option - but even without it, the system will be gameable as long as "Hide all new images unless they have been OK'd by a fellow filterer with similar preferences to me" exists as an option. Yet, that is the most powerful and potentially most popular option.
I had typed out a long description of precisely how this might be gamed here, but I started boring even myself, so let me just state the principle: if you create enough accounts that have preferences matching a particular statistical user cluster (easy to do by blocking all images of Mohammed), you can exercise disproportionate statistical control over which new images those real users see by having your army of ringers deliberately green-light new images.
Well of course any of the editors could themselves have the filter set on
and would know what the score was relative to their preferences. But otherwise the information would be secret. I don't see how we could give editors access to the reputation information without it leaking to censors, or indeed divulging it generally.
Although the per-user score might be the important one for the operation of the algorithm, it's obvious that per-image data will exist, or at least could be calculated. We *could* calculate statistics for each image like "likelihood of actually being seen by a viewer" without revealing any personal information. It would also be possible to show "likelihood of being seen by readers who have blocked image X" for image Y.
This information *could* be useful to censors, but if it was available only to logged-in users it would be practically difficult for them to access in an automated manner.
As for "legitimate editorial reasons", I think it would be quite contentious if anyone started making editorial decisions based on the filter results, so best not to enable that - but I'll clarify that in the proposal
I certainly don't think it would be more contentious than having the filter in the first place! There are certainly legitimate editorial reasons for wanting to know some of the information I mentioned. I personally believe that images are content, that they hold information, and that they are not mere decoration in an article. There are plenty of situations where the question "what percentage of readers of this page will not be shown this image" would inform the decision about whether to use the image at all, and inform decisions about the wording of the article copy.
Anyway, as I have said, I think your basic idea here is the only practical option if a filter is to be implemented. I am personally not in favour of doing so, for both idealistic and practical reasons (specifically, the amount of effort it will involve vs. the amount of benefit it will deliver, with special consideration for the fact that almost no one seems to have asked for an opt-in filter, but rather for Wikipedia just not to have those images in the first place).
Be all that as it may, if we are to have a filter, we need to have a working filter. We need to have the best filter we possibly can, with the least increase in workload for editors and the most functionality for readers. In my opinion the system you have outlined is not only the best option so far, but also the best option possible. I do encourage others to read your design (http://meta.wikimedia.org/wiki/User:WereSpielChequers/filter) and to get involved in figuring out how it might work.
Cheers,
Andrew (Thparkth)