Hi John, thanks for your help! So, I noticed I had an inconsistency here with the field name:
<?php
// Get the logo, if it exists.
$image = get_field('sponsor-logo');
if( get_field('sponsor_logo') ): ?>
Having fixed that and changing the image tag to your suggestion now seems to put the image ID in the SRC – for example:
<img class="sponsorlogo" src="266" width="120" height="120" alt="Hillcrest Paving & Excavating">
I’ve checked the field setup itself and it is set to output a URL, and does so in other templates. I’m guessing that because this template is for tags of a custom post type, it might require something else?
