don't bother, I've already found out:
<img loading="lazy" class="<?php echo (bet_is_lazy() ? 'lazy' : ''); ?>" src="<?php echo (bet_is_lazy() ? bet_get_noimage() : '/imageexample.jpg'); ?>" data-src="/imageexample.jpg" alt="imageexamplename">
This is important for the images that we have in the footer, since they will not load until they are shown on the screen.
That way, the web loads much faster, because it loads the images / no-image.png image until the user downloads the scroll to the footer.