首先，当你打电话给get_image 函数将post categories slugs作为参数传递。

Edit 你的autoset_featured 作用replacing

...
} else {
   set_post_thumbnail($post->ID, get_image());
}
...

使用：

... 
} else {
  $cat_slugs = wp_get_post_terms($post->ID, \'event-categories\', array("fields" => "slugs"));
  $image = get_image( $cat_slugs );
  if ( image ) set_post_thumbnail($post->ID, $image);
}
...

然后编辑get_image 对这样的事情：

function get_image( $cats = array() ) {
  $media_query = new WP_Query(
    array(
      \'post_status\' => \'inherit\',
      \'post_parent\' => 0,
      \'post_type\' => \'attachment\',
      \'post_mime_type\' => \'image/jpeg\',
      // set \'orderby\' to \'rand\' will randomize results order
      \'orderby\' => \'rand\',

      // READ CAREFULLY:
      // if in the title of all images intended to be used as thumbnail
      // you put something that contain \'UF\' you can use the \'s\' param
      // retrieving less results and so improving performance
      // in that case uncomment next line
      // \'s\' => \'UF\'

    )
  );

  if ( $media_query->have_posts() ) {

    $lastid = false; // just an early setup

    // loop through images
    foreach ($media_query->posts as $post) {

      // get current image url
      $fullpath = wp_get_attachment_url($post->ID);

      // if current image name doesn\'t start with \'UF-\' skip it
      if ( strpos( basename($fullpath), \'UF-\' ) !== 0 ) continue;

      // if the original post has no categories assigned, return first image ID
      // images are random ordered, so first one is random one
      if ( empty($cats) ) return $post->ID;    

      // get current image file name (without extension) and remove the \'UF-\' part
      $name = pathinfo( basename($fullpath), PATHINFO_FILENAME);
      $nameNoUF = str_replace(\'UF-\', \'\', $name); 

      // $nameNoUF contain something like \'category-name-01\'
      // because \'UF-\' at beginning and extension were both removed

      // save the current image ID in a helper variable for future possible use
      $lastid = $post->ID;

      // loop through categories and if $nameNoUF start with a category slug,
      // return the image ID.
      // this way every image named like \'UF-category-name-01.jpg\' match
      foreach ( $cats as $cat ) {
        if ( strpos($nameNoUF, $cat) === 0 ) return $post->ID;
      }
    }
    // if we are here no category related image was found, so return the last image ID
    // images are random ordered, so last one is random one
    return $lastid;
  }
  // no images found at all, sorry, return false (no thumbnail will be setted)
  return false;
}

按照内联注释中的建议，使用s 用于检索标题或内容中包含“UF”的图像以限制结果的查询中的参数。当然，这需要您将该字符串添加到图像标题或内容中。

内联注释应该解释函数的工作方式。

希望有帮助。