TinyMCE WordPress Plugin Clickable Image

Should be a matter of extending TinyMCE valid elements in your own plugin. Here is an example of adding an image tag with all attributes enabled:

add_filter( 'tiny_mce_before_init', function ( $init ) {
    $img = 'img[*]';
    if ( isset( $init['extended_valid_elements'] ) ) {
        $init['extended_valid_elements'] .= ',' . $img;
    } else {
        $init['extended_valid_elements'] = $img;
    }
    return $init;
});

The following content was used when inserting the following into the post content when creating the TinyMCE button :<img>

ed.addButton( 'test_button', {
    title : 'Insert clickable image',
    image : '../wp-includes/images/smilies/icon_eek.gif',
    onclick : function() {
        ed.selection.setContent( '<img src="http://example.com/test.gif" onclick="alert()" />' );
    }
});