Here are two filter examples:


    add_action( 'pre-upload-ui', function() {  
        ?><h4><?php _e( 'Please Remember This And That! (pre-upload-ui)' );?></h4><?php 
    });
    
    add_action( 'post-upload-ui', function() { 
        ?><h4><?php _e( 'Please Remember This And That! (post-upload-ui)' );?></h4><?php 
    });

This will show up as:

[![Notices][1]][1]


  [1]: https://i.sstatic.net/MDiOI.jpg