example.html.erb

<!-- UPDATE THE :image => @example.image PART TO REFLECT YOUR MODEL AND ATTRIBUTE -->
<div class='field'>
      <%= f.label :image -%>
      <%= render :partial => "/shared/admin/image_picker", :locals => {
        :f => f,
        :field => :image_id,
        :image => @example.image,
        :toggle_image_display => false
      } %>
    </div>