'roll-over' logo in footer.php

hello!

short question, maybe someone can help:
the bmwl-logo should appear as a ‘roll-over’-link in the footer of website – but it does not.

where else do I have to embed code than in footer.php?

wp-site: https://cash-security-tec.de

code:

<a href="https://www.gs1.org/">
                <img class="color-image" src="<?php echo get_template_directory_uri(); ?>/assets/img/logo-gs1-grayscale.png" alt="GSI">
                <img class="gray-image" src="<?php echo get_template_directory_uri(); ?>/assets/img/logo-gs1.png" alt="GSI">
            </a>
		<a href="https://www.wertelogistiker.de/">
			<img class=colour-image" src="<?php echo get_directory_uri(); ?>/assets/img/logo-BMWL-grayscale.gif" alt="BMWL">
			<img class="gray-image" src="<?php echo get_directory_uri(); ?>/assets/img/logo-BMWL.gif" alt="BMWL">

Thanks for taking care of this!

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