<%= form_tag(search_pictures_path, method: :get, enforce_utf8: false, class: 'search') do %>
  <div class="input-group">
    <%= search_field_tag :q, params[:q], placeholder: 'Search pictures...', class: 'form-control', 'aria-label' => 'Query' %>
    <span class="input-group-btn">
      <button class="btn btn-secondary" id="search-submit" aria-label="Search">
        <%= fa_icon('search') %>
      </button>
    </span>
  </div>
<% end %>

<%= form_tag(search_pictures_path, method: :get, enforce_utf8: false, class: 'search') do %>
  <div class="input-group">
    <%= search_field_tag :q, params[:q], placeholder: 'Search pictures...', class: 'form-control', 'aria-label' => 'Query' %>
    <span class="input-group-btn">
      <button class="btn btn-secondary" id="search-submit" aria-label="Search" style="cursor:pointer">
        <%= fa_icon('search') %>
      </button>
    </span>
  </div>
<% end %>

Change cursor on search button
Change cursor on search button
