How to set featured image as background for a specific category?

Question

I am currently trying to set the most recent post's featured image to be the background of my hero image. This is the code I'm using:

<?php $backgroundImg = wp_get_attachment_image_src( get_post_thumbnail_id($post->ID), 'full' );?>

Problem is, it shows the featured image of the most recent most on the entire site. I'm trying to make it use the most recent featured image from a specific category (ID is 42). Could I do something like this:

<?php $backgroundImg = wp_get_attachment_image_src( get_post_thumbnail_id($post->ID;cat="45"), 'full' );?>

Answer 1

I am not sure where you are trying to do this but give something like this a try.

<?php 
    $category_id = 45;
    query_posts('showposts=1&cat='.$category_id);
    if (have_posts()) : while (have_posts()) : the_post(); 
        $backgroundImg = wp_get_attachment_image_src( get_post_thumbnail_id($post->ID), 'full' );
    endwhile; endif;
    wp_reset_query(); 
?>