app/views/yandex_captcha/_captcha_ajax.html.erb
<div id="captcha_widget" data-api="<%= yandex_captcha.captcha_path %>">
<div id="captcha_image">
<img src="<%= asset_path("yandex_captcha/loading.gif") %>" />
</div>
<input type="text" id="captcha_response_field" name="captcha_response_field" placeholder="Введите цифры" />
<input type="hidden" name="captcha_response_id" value="" />
</div>
<%= javascript_include_tag "yandex_captcha/captcha" %>