Retrieve uploaded image attibutes value from option tree theme options

Put this code in index.php

---

<img class="img-resposive" src="https://wordpress.stackexchange.com/questions/218286/<?php 
    $logo=get_option_tree("logo','','true'); // return src of img
    $id_logo = get_attachment_id_from_src($logo); // This is custom  function for getting image id.
    $alt = get_post_meta($id_logo, '_wp_attachment_image_alt', true);// get alt="" from wordpress media.
    if ( function_exists( 'get_option_tree') ) : 
        if( get_option_tree( 'logo')) :             
            $logo;  
        else:
             echo bloginfo('template_directory') .'/assets/images/logo_vp.png'; // else if option is empty get this image.
        endif;  
    endif;  
?>" alt="<?php echo $alt; ?>"/>

Put this function code in functions.php

//get id from image source
function get_attachment_id_from_src ($image_src) {
    global $wpdb;
    $query = "SELECT ID FROM {$wpdb->posts} WHERE guid='$image_src'";
    $id = $wpdb->get_var($query);
    return $id;
}

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This code is tested. Working fine.