If a wiki project wishes to add a filter category that doesn't exist on Commons, they have to host the images locally, then add them to their project's filter category. So the implication of this is that a project must host copies of images that it wishes to hide !!? Eg, if Commons did not have a filter category for images of Prophet Mohamed then a project that wants to hide them would have to host all such images so that it could then hide them. ... I can see this could be a real problem! Equally projects that don't allow local uploads would have a problem.
Topic on Talk:Personal image filter
I think you're overdoing it a little bit here.
Back to the beginning of your post:
"If a project wishes to filter a category that doesn't exist on Commons".
If the category does not exist, you can not filter it with a category. That's obvious.
The rest after that sentence doesn't make any sense. Commons is freely editable, if a category doesn't exist, you can create it. Re-uploading locally makes no sense, you're right, so let's not do that :-)
Not if there's a standing policy against the existence of a specific category. For example, there are some people who consider non-free media used under an EDP to be offensive. See, for example, w:WP:Veganism parable and Kusma's comment in meta:Talk:Image_filter_referendum/en#Hiding the Pokemon Logo as Inappropriate Content... Really?. But there is obviously no category for non-free media in Commons because Commons doesn't allow non-free media.
I am not sure whether you are just complaining about my wording, or do not understand the point. I will rephrase: The proposal is to filter based on both special filter-categories on Commons and on local wikis (because not all images are on Commons). If a local wiki wishes to exclude images based on some criteria (ie a whole class or category of images based on some local criteria not included in the Commons filter-categories, eg images of the Prophet), they will have to make local copies of those images so they can add them to their own exclusion category. Does that make sense now? --Tony Wills 23:09, 9 August 2011 (UTC)
I'm sorry, but I think we are both not understanding each other's point.
My point was that if a user of a wiki wishes to filter on a category that doesn't exist on Commons, you can create one. To repeat your example, if there is no category on Commons like "Images of X", you can create such a category – on Commons.
Krinkle: An editor from a wikipedia can create a category on commons, sure. But Commons has its own "consensus" and it may be against having this category. That's the problem: local wikipedias going against "consensus" on commons, local wikipedias in war with other wikpedias etc... How about Category:Armenian POV stuff banned from Azeri wikipedia and Category:Azeri POV stuff banned from Armenian wikipedia ? Do the have any chances of staying on commons? NVO 05:17, 16 August 2011 (UTC)
No, one can't necessarily create a category on Commons for filtering if the subject matter of the category is things that are specifically disallowed on Commons. --Damian Yerrick 11:28, 28 August 2011 (UTC)