pgadmin4/web/pgadmin/templates/security/watermark.html

{% block watermark %}
<div style="position: fixed; bottom: 0; right: 0;">
    <img src="{{ url_for('static', filename='img/logo-right-256.png') }}"
         alt="{{ config.APP_NAME }} {{ _('logo') }}"
    >
</div>
{% endblock %}