I'm currently using this code which adds a header on the post profile.

Code:

.topic-author {
  background: #fff;
  float: none;
  width: auto;
  text-align: left;
  position: relative;
  padding: 10px;
  background: url("http://i.imgur.com/H1KP8Z0.png");
}

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Forum version: PunBB

I'd like to make it for a certain user ID. Any help?

You can try this code:

Code:

$(function() {
  var userlist = ["u1","u2"]; // all the user id's that need the special background
  $('.post').each(function() {
    var userID = $(this).find('h4.username a:first').attr('href').substr(1);
    if (jQuery.inArray(userID, userlist) !== -1) {
      $(this).find('.topic-author').addClass('special');
    }
  });
});

On top you need to insert al the userid's of who need to have that background, then script will add the class special to the element with the class topic-author. So you need to set your css to

Code: .topic-author.special

.