In the one of my projects which is already using the ScreenshotsPlugin, I granted SCREENSHOTS_VIEW to anonymous. Being not logged in, I can see the screenshots in the Wiki articles. But going to the plugins page ("/screenshots"), there's only an empty page displayed. Only after I add SCREENSHOTS_FILTER, anonymous visitors have a chance seeing the screenshots - since the default is "nothing selected". Even if I add all components to "default_components", without the "SCREENSHOTS_FILTER" permission there is still nothing displayed. I don't think this is intended - is it?
IMHO, without the SCREENSHOTS_FILTER permission (but the SCREENSHOTS_VIEW permission) granted, a visitor should see screenshots of the components defined in "default_components". And, BTW: How about the keyword "all" in default components? It is very unlikely somebody will use a component like that - but if I add a new component, I may forget about updating the default_components ;)