This is a common issue experienced by most WordPress users who often upload, insert, edit and drop lots of images on their WordPress websites.
The main problem is when your delete an image from the WordPress media library, it still show up in your posts on fronted. The question is how can you get the images that you have already deleted from your website.
Some bloggers select hard way of editing each individual post to remove pre-delete images one by one. But that’s not the easy solution.
Actually this problem is not a problem but a cache issue, even if you are not using any cache plugin WordPress has built-in cache functions and also the web-browsers.
Another reason is CDN, if you are using CDN then your images shows up from the URL of your content delivery network.
Inserted images are output with code in the content area for posts, pages and other custom post types. If the code is not removed, it will show cached content for a while, then eventually a broken image symbol.
So all you have to do is clear cache your website’s cache (if using a cache plugin), your web browser’s cache, keep patience and wait.
For image galleries embedded in your content, you may delete unwanted images from the media library and they will also be automatically removed from whatever gallery(‘s) they are included in.