Broken links in search results
Sometimes after we find an image something changes so that it is no longer accessible. This could happen because the image file has been moved or deleted, or even because the entire site no longer exists. This is a common occurrence as the web is constantly changing.
In general, we don't remove images from our search index when they're removed from the site they're found on. This information helps validate where an image originally came from on the internet and can be useful for certain types of research.