TwentyFifteen creates post thumbnails from the first image it finds in page media.
Blogitem.html.twig:
<div class="post-thumbnail">
{{ page.media.images|first.cropZoom(1038,437).html(page.title, page.title, 'attachment-post-thumbnail wp-post-image') }}
</div>
Is it possible to customize this theme so that the post thumbnail is an image stored in /pages/images and selected manually e.g. in frontmatter?
I suspect some of my posts may use the same image as a post thumbnail, so would like to avoid duplicating the same image file across different posts.
Thank you in advance!