This looks like a lazy image loading technique. The more modern way of doing this is using the standard HTML
If you right-click on the page and use ‘View page source’ you’ll likely see different attribute values for this element than you’d see using the browser’s developer tools. That’s what Full-Text RSS sees too.
We do handle some common lazy loading techniques in Full-Text RSS, but this doesn’t cover all cases. So sometimes a custom site config file is needed to fix things up.
If you have the page URL, we’ll be happy to look into it.