Use post_tags

@rickvandeven,

Um, no. You don’t need Media-Tags then. Just set the post_tags and use the built-in WordPress functions.

But there is a difference. Let me try and explain. When you create a Post and assign a post_tag you create that relationship. For images which are attachments, WordPress does not provide any method to classify these into categories/tags. This is where Media-Tags comes into play. It allows you to associate a media-tag (similar to post_tag) with an attachment.