no image preview kanban view Odoo 8

Hello
I made a simple costume module and kanban view. but the image is not previewing.
this is my code am i doing it wrong? the empty avatar from base/static is showing fine.

 <?xml version="1.0"?>
<kanban>
                    <field name="name"/>
                    <field name="image"/>
                    <field name="f_name"/>
                    <field name="reg_number"/>
                    <field name="phone"/>
                    <field name="email"/>
                    <templates>
                        <t t-name="kanban-box">
       <div class="oe_kanban_vignette oe_semantic_html_override">
         <div>
          <a type="open">
          <t t-if="record.image.raw_value === true">
           <img t-att-src="kanban_image('students.mgmt', 'image', record.id.value)" class="oe_employee_image"/>
           </t>
          <t t-if="record.image.raw_value === false">
           <img t-att-src="_s + &quot;/base/static/src/img/avatar.png&quot;" class="oe_kanban_image"/>
           </t>
          </a>

         <div class="oe_kanban_details oe_kanban_box_content oe_kanban_color_bglight oe_kanban_color_border">
         <h4><a type="open"><field name="name"/></a></h4>
                                    <ul>
          <li><field name="f_name"/></li>
          <li><field name="reg_number"/></li>
          <li><field name="phone"/></li>
          <li><field name="city"/> <field name="country_id"/></li>
          <li><a t-attf-href="mailto:#{record.email.raw_value}"><field name="email"/></a></li>
         </ul>
         </div>
         </div>

       </div>
                        </t>
                    </templates>
                </kanban>

in the module.py
image = fields.Binary()