Header images should use get_header_image_tag()

[raamdev]

Currently, the <img> tag for the header image is built manually in independent_publisher_posted_author_card():

independent-publisher/inc/template-tags.php

Line 491 in 36dd2c2

<img class="no-grav" src="<?php echo esc_url( get_header_image() ); ?>" height="<?php echo absint( get_custom_header()->height ); ?>" width="<?php echo absint( get_custom_header()->width ); ?>" alt="<?php echo esc_attr( get_bloginfo( 'name', 'display' ) ); ?>" />

It would be better to use get_header_image_tag() to build this tag, as that will include the srcset attributes for responsive images automatically.