Issue: Empty attachment box displayed

It is not recommended to post images that a user can't view inside content that the user can view. Since it is not practical to check the user's image permissions when rendering the content (due to caching and expense), instead we should show a stock image representing that the requested image is not allowed or available. This presents issues with empty frames/borders when a caption is not provided. Will try to put these error-images into 4.1.x.

I don't think this is a sound solution. Its standard forum behavior to not display anything if the user does not have attachment permissions.
It was possible in VW3. Why not in VW4? If I embed a forum image into a wiki then it will not display if the user has no permission. VW should do the same.

Lazy loading is new in VW4 and lazy-loading an image requires that all content above it has a known height (even if the content contains another image that would be lazy-loaded) or the loader will miss when the image has scrolled into view. This requires us to define the height of the image container before the image is lazy-loaded and to enforce that the height not change after loading has completed (lest later lazy-loaded images be shifted and mess up the calculations).

We can add a setting allowing admins to disable the lazy-loader, but it really saves a lot of bandwidth.

There is a lazy load addon for xenforo. IIRC it doesnt display empty boxes. If a XF attachment is missing then nothing is displayed. Maybe the same approach could be useful for VW?
https://xenforo.com/community/resour...load-img.3979/

For my site the bandwidth cost is irrelevant (we use cloudflare)
Site speed is important, which is why I will probably turn the above addon on again.

Another issue I see with lazy-loading without known heights is that if 1000 images are in a row with no text, they will all be in the viewport before they are loaded, so all 1000 images would start loading even if they would be pushed out of view by the final heights of the adjacent images. I think this might be an issue for the underlying library in the add-on you linked, which only seems to implement a time-based throttle.

If we add an option for allowing unknown heights in VW, we will have to implement a counter-based throttle like only having a maximum of 10 lazy-load slots at any time.

In the end, I think we would make this an option; whether you want un-loadable images hidden, whether you want an error-image used, or whether lazy-loading should be disabled.

That would be good.

This is marked as fixed in the next release.

In the next release, a new VaultWiki: Aesthetics option:
Lazy load wiki attachment images?
0 - No
1 - Yes, using fixed heights, loading indicators, and error notices. (default)
2 - Yes, using browser-default size before loading and on errors, with a throttle.

When there is a problem loading the image:
#1 will use CSS to render a relevant error icon, and the alt text is changed to a relevant error message (like "You do not have permission...", "Resource not found", etc).
#2 will just use the browser default for failed images, which might be a 0x0 render, or might be a small red X. As I discussed above, since this would make the document height unknown, we have a lazy-load queue that can only contain 10 images at a time, recalculating the height after each image. This prevents all images from loading at once when later images might end up off-screen after an earlier image loads.