Hi,

First extend Actionpad widget template(pos.xml) and replace class “set-customer”

<button t-attf-class='button set-customer #{ ( widget.pos.get_client() and widget.pos.get_client().name.length > 10) ? "decentered" : "" }' >
    <t t-if="widget.pos.get_client()">
        <img t-att-src='widget.partner_icon_url(widget.pos.get_client().id)' style="height: 80% !important;" />
        <t t-esc="widget.pos.get_client().name" />
    </t>
    <t t-if="!widget.pos.get_client()">
          <i class='fa fa-user' />
        Customer
    </t>
</button>

Extend Actionpad widget with a new function (screen.js)

partner_icon_url: function(id){
        return '/web/image?model=res.partner&id='+id+'&field=image_small';
    },

Thanks