Customize page 404

mm @marouane87 you invented “tc_show_image” and “tc_image_name_id” that’s why nothing happens.
Nicolas’ snippet was to show a slider in that page, create a slider and use that snippet.
Do you want something like:
[slider]
[missing page alert]
[search]
?

Try this then,

add_filter('tc_404_content', 'my_404_content');
function my_404_content(){
    $image_url = 'REPLACE THIS WITH YOUR IMAGE URL';
    return sprintf('<img alt="Not Found" class="404-img" src="%1s">%2$s',
        $image_url,
        get_search_form( $echo=false)
    );
}

You’re welcome.
Just add also this to your child-theme functions.php

add_filter('tc_no_result_content', 'my_404_content');

This will point to the same function my_404_content.

Oh great you took a look at the hooks api 😀
( You’re on the right track… so don’t delude me 😛 )

Unfortunately the hook tc_no_results_content_icon, as the name suggests, is about an icon you already don’t display because we get rid of the original content with the code I posted above.
You’re interested about some Headings filters like:

add_filter('tc_search_results_header_content', 'change_search_title');
function change_search_title($header){
    /* with this if you change the search title when there are no results */
    if ( is_search() && ! have_posts() ){
       $new_title= '<h1>My New No result title</h1>';
       return preg_replace('|<h1.*?</h1>|', $new_title,$header);
    }
    return $header;
}