zulip/web/templates/message_avatar.hbs

<div class="u-{{msg/sender_id}} message-avatar sender_info_hover view_user_card_tooltip no-select" aria-hidden="true" data-is-bot="{{sender_is_bot}}">
    <div class="inline_profile_picture {{#sender_is_guest}} guest-avatar{{/sender_is_guest}}">
        <img loading="lazy" src="{{small_avatar_url}}" alt="" class="no-drag"/>
    </div>
</div>
{{~! remove whitespace ~}}