Part of the answer here : https://www.odoo.com/fr_FR/forum/help-1/question/adding-i-frame-in-openerp-34242

 **`Image Url wise Set Dynamic Iframe In Odoo`**
# v11 odoo community
you need to create  fields like this :
image_url = fields.Char('Image Url')
img_attach = fields.Html('Image Html')


# set image_url in iframe
     @api.onchange('image_url')
     def onchange_image_url(self):
         if self.image_url:
             self.img_attach = '<img id="img" src="%s"/>' % self.image_url


# set image_url in form view     
        <field name="image_url" />


# after added script
        <script>
        if(document.getElementById("img")){
           var value= document.getElementById("img").src;
           document.getElementById("custom_src").src=value; 
         }
        </script>


# also set iframe in form view
      <iframe id="custom_src" src="" width="200" height="200"  />     

#output
show the image : https://i.stack.imgur.com/0x7et.png