On front end of page I use img tag for display binary image from database.
<img t-att-src="'data:image/png;base64,%s' % task.image" />
How hide tag if value is empty, now in my solution display small square.
http://imgur.com/a/ZATb9
<t t-if="task.image"> <img t-att-src="'data:image/png;base64,%s' % task.image"/> </t>