Native WordPress tag for images in library

I’m trying to use a front end search plugin the requires images to be tagged by the WordPress tags. I’ve used a couple plugins to tag images, without success. How do I tag images in the Media Library without a plugin?

Here’s the requirements;

What are the prerequisites to run this plugin ?
At least one media should be present in your blog. Otherwise the MediaTagger admin panel will inform you that you need to start working on your blog !
Same comment for the tags declared in your blog.
How are defined the tags proposed for the media classification ?
By default the plugin will use the WordPress tags. Anyhow you can decide to use WordPress categories instead, or to combine tags and categories.