Hi nitzanginsberg,

The plugin does not support tags and categories in the interface.
But you can tweak your own:

function dfi_tag( $dfi_id, $post_id ) {
	// all which have 'animals' as a category.
	if ( has_tag( array( 'cats', 'dogs' ), $post_id ) ) {
		return 8; // image ID for cats or dogs .
	} elseif ( has_tag( 'chicken', $post_id ) ) {
		return 9; // image ID for cats or dogs .
	}

	return $dfi_id; // the original featured image id
}
add_filter( 'dfi_thumbnail_id', 'dfi_tag', 10, 2 );

If you insert this in your theme’s functions.php (or in a separate mu-plugin). it will set a different image for cats and dogs. And another different image for chickens.

Let me know how it goes.
Jan Willem