Users can add images to content. They're supposed to be uploading them to the site, but occasionally people will reference an image hosted elsewhere in the src='...'.
What is the best way to prevent these images from working (or even better, redirecting to a "This image is blocked" image)? I imagined using a hook of some sort to modify the content, or possibly a module that adds a filter to weed out these images. But it seems like a situation I could be overthinking.