The implementation can be purely CSS, and depends on your specific HTML markup. However, the class you’ll need to target is supplied by the post_class()
template tag.
Let’s say you have something like the following, basic markup:
<div id="post-<?php the_ID(); ?>" <?php post_class(); ?>>
<div class="post-title">
<img ... />
<h1><?php the_title(); ?></h1>
</div>
<!-- Etc. -->
</div>
The post_class()
template tag will output a category-based class, category-{name}
, and also, category-{id}
. So, you can target either one in your stylesheet:
.category-{name} .post-title img {}
or
.category-{id} .post-title img {}
It’ll be specific to your markup, of course; but hopefully you get the idea.