I am trying to improve the LCP load time on my wordpress website. The featured image is what is causing the issues, so my plan is to use: <picture> <source srcset=image.png" media="(min-width: 1280px)"> <source srcset=image2.png" media="(min-width: 768px)"> <source srcset=image3.png" media="(min-width: 412px"> </picture> So the web browser will pick the correct size of image based on the device being used. Wordpress by default has different image sizes I can use. So I want to pull in the different image sizes like so: <?php if ( has_post_thumbnail($post->ID)) { ?> <div class="hero-flex-col"> <?php global $post; $mime_type = explode('/', $type); $type = '.'.$mime_type['1']; $img_alt = get_post_meta( $image_id, '_wp_attachment_image_alt', true ); $image_id = get_post_thumbnail_id($post->ID); $img_full = wp_get_attachment_image_url( $image_id, 'full'); $img_large = wp_get_attachment_image_url( $image_id, 'large' ); $img_medium_large = wp_get_attachment_image_url( $image_id, 'medium_large' ); $img_medium = wp_get_attachment_image_url( $image_id, 'medium'); ?> <picture> <source srcset="<?php echo $img_large; ?>" media="(min-width: 1280px)"> <source srcset="<?php echo $img_medium_large; ?>" media="(min-width: 768px)" type="image/<?php echo $mime_type['1']; ?>"> <source srcset="<?php echo $img_medium; ?>" media="(min-width: 412px)" type="image/<?php echo $mime_type['1']; ?>"> <source srcset="<?php echo $img_medium; ?>" media="(min-width: 360px)" type="image/<?php echo $mime_type['1']; ?>"> <source srcset="<?php echo $img_medium; ?>" media="(min-width: 0px)" type="image/<?php echo $mime_type['1']; ?>"> <img src="<?php echo $img_medium; ?>" fetchpriority="high" alt="<?php echo $img_alt; ?>" style="min-height: 180px;" width="640" height="360"> </picture> </div> <?php } ?> The issue I have is that wp_get_attachment_image_url only ever pulls the default image url. I have tried also to regenerate the thumbnails using the following plugin and it makes no difference: https://en-gb.wordpress.org/plugins/regenerate-thumbnails-advanced/ I've been pulling my hair out for days on this one so would really appreciate someones help.