insert image by src <img src=" " />

// img src for

								<img src="<?php
								$thumb_id = get_post_thumbnail_id();
								$thumb_url = wp_get_attachment_image_src($thumb_id,'promo_img_size', array('class' => 'promo_portfolio', true));
								echo $thumb_url[0];
								?>" alt="" />


/*****************************and usages in shortcode**********************************************/

// usages of news ticker as a shortcode

if(! function_exists('owl_carousel_shortcode')):
function owl_carousel_shortcode($atts){
        extract( shortcode_atts( array(
                'category' => '', // category by default
                'count' => '10' // default post 10
        ), $atts, 'items_do_shortcode' ) ); // this is for do_shortcode where we have to query(to show post)

    $q = new WP_Query(
        array('posts_per_page' => -1,
				'post_type' => 'owl_post', // custom post type
				'category_name'=>$category,
				//'order'=>'ASC'  //this is for price order

					)
                );


        $list = '<div class="owl-demo">'; // wrapper will go here
        while($q->have_posts()) : $q->the_post();
		$thumb_id = get_post_thumbnail_id();
		$thumb_url = wp_get_attachment_image_src($thumb_id,'owl-carousel-size', array('class' => 'promo_portfolio', true));
              $list .= '
				<div class="item"><img src="'.$thumb_url[0].'" alt="hello"/></div>
			  ';
        endwhile;
        $list.= '</div>';
        wp_reset_query();
        return $list;
}
add_shortcode('owl_carousel','owl_carousel_shortcode');