erpnext/templates/emails/birthday_reminder.html

<div class="gray-container text-center">
	<div>
		{% for person in birthday_persons %}
			{% if person.image  %}
			<img
				class="avatar-frame standard-image"
				src="{{ person.image }}"
				style="{{ css_style }}"
				title="{{ person.name }}">
			</span>
			{% else %}
			<span
				class="avatar-frame standard-image"
				style="{{ css_style }}"
				title="{{ person.name }}">
				{{ person.name[:1] }}
			</span>
			{% endif %}
		{% endfor %}
	</div>
	<div style="margin-top: 15px">
		<span>{{ reminder_text }}</span>
		<p class="text-muted">{{ message }}</p>
	</div>
</div>