Re: message can contain images, videos and rich text
check out this plugin:
Why the need of a preview box if you have the What You See Is What You Get Editor in the same place as your visitors type in the comments?
This plugin turns the comment field from a primitive into a WYSIWYG editor, using the internal TinyMCE library bundled with WordPress 2.0 or up, without the need of another separate installation. Functions that only available to writers like adding images were removed and will not show up in the toolbar.
If you add to the mu-plugins and add this line to the end of the plugin file:
This is only the concept, I have not tested it, and don’t have the time but wanted to point you in a direction.