JOOMLA-ROOT/layouts/joomla/content/intro_image.php
to
JOOMLA-ROOT/templates/<YOUR_TEMPLATE>/html/layouts/joomla/content/intro_image.php
Then, edit the code in that new override file by wrapping the image tag with:
<a href="/<?php echo JRoute::_(ContentHelperRoute::getArticleRoute($displayData->slug, $displayData->catid)); ?>" itemprop="url"> </a> The <img> tag will have a bunch of php code in the middle of it, so you have to figure out where the end is and place the closing anchor tag after that.


