app/views/web_admin/images/_images.html.erb
<% album.images.order("id asc").in_groups_of(6, false).each do |image_group| %>
<% image_group.each do |image| %>
<div class="col-md-2">
<span><%= flash[:notice] %></span><br />
<%= image_tag image.file.url(:thumb_admin) %><br />
<%= check_box_tag :cover, image.id, image.cover?, class: "cover" %>
</div>
<% end %>
<% end %>