Custom CSS to hide image title

Hey Renaud,
If you are not using a child theme you could use the WP Code plugin then add a new snippet, in the top right corner use the PHP snippet as the code type:

and ensure that it is activated, then add this code and save.

function custom_script() { ?>
  <script>
(function($){
  $('img').hover(function(e){
      $(this).attr('data-title', $(this).attr('title'));
      $(this).removeAttr('title');
  },
  function(e){
      $(this).attr('title', $(this).attr('data-title'));
  }); 
  $('.av-masonry-image-container').hover(function(e){
      $(this).attr('data-title', $(this).attr('title'));
      $(this).removeAttr('title');
  },
  function(e){
      $(this).attr('title', $(this).attr('data-title'));
  }); 
  $('a').hover(function(e){
      $(this).attr('data-title', $(this).attr('title'));
      $(this).removeAttr('title');
  },
  function(e){
      $(this).attr('title', $(this).attr('data-title'));
  }); 
})(jQuery);
</script>
  <?php
}
add_action( 'wp_footer', 'custom_script', 99 );

Best regards,
Mike