Php 如何获取home类别中的特定alt标记

如何在这段代码中获得alt image标记

我不知道我做了什么，在这段代码中，请帮助我如何才能获得类别的特定alt标记图像

谢谢。。wordpress的新手

<div class="home-content-wrapper-preview">

<?php

    $paged = get_query_var('paged') ? get_query_var('paged') : 1; //Use 'page' instead of 'paged' if you are on home page
    $Preview = get_theme_mod( 'Preview');
    $args = array(
    'category_name'          => $Preview,
    'post_type' => 'post',    //Selecting post category by ID to show
    'posts_per_page' => 6,    //Eexcluding latest post
    'paged' => $paged         //For pagination
    );

    $loop = new WP_Query( $args );

    while ( $loop->have_posts() ) : $loop->the_post();
    $index= $loop->current_post + 1;

    if ( has_post_thumbnail() ) {
    $featured_img_url = get_the_post_thumbnail_url(get_the_ID(),'full'); }

    else{
    $featured_img_url = "".get_template_directory_uri() ."/placeholder.jpg";
    } // get the defualt poster image when you forgot to put

    $content = get_the_content();

    echo "<div class='preview".$index."'>

    <img src='".esc_url($featured_img_url)."'/>

    <div class='post-inner'>
    
    <h2 class='entry-title'> <a href='".get_permalink( $post->ID )."'>".$post->post_title."</a></h2>

    </div>

    </div>";

    endwhile; 


?>
  

</div>