There's no perfect way to check whether an image or document (or a page on your site) isn't being linked to from elsewhere, and unfortunately Voice doesn't keep track of this.

Indeed, a page or document could be linked from somewhere else on the Internet which you have no control over. So even if you don't have a link to it on your site, it may be referenced from elsewhere.

One thing you could do is to check in the Reports tab of your site to see if the image/document is being viewed. If it has zero hits then it's a safe bet that it's not being used anywhere!

Thanks

Joe