How to output an image or icon for selected check box in a custom post

You can do this by custom meta, all you have to do create custom metabox and the your checkboxes on it, the easiest way to create custom metabox is

1). Download WP Alchemy Metabox Class from here

2). Palce ‘wpalchemy’ folder inside of your theme folder

in your function.php file

include_once WP_CONTENT_DIR . '/themes/yourtheme/wpalchemy/MetaBox.php';

3). after that, create two php files by following names ‘my-special-feature-meta.php’ , ‘my-special-feature-spec.php’ (you can name your php files whatever you want).

in your ‘my-special-feature-spec.php’ file

<?php
global my_special_features; 
$my_special_features = new WPAlchemy_MetaBox(array
(
    'id' => '_my_special_features',
    'title' => 'Special Features',
    'template' => get_stylesheet_directory() . 'my-special-feature-meta.php',
    'types' => array('page','post','your_custom_post')
));

/* eof */

and your ‘my-special-feature-meta.php’ file

Group checkbox test #1

<?php 
 global $my_special_features;
 $items = array('internet', 'laundry', 'garage', 'tv'); 
?>

    <?php while ($my_special_features->have_fields('cb_ex', count($items))): ?>

        <?php $item = $items[$mb->get_the_index()]; ?>

        <input type="checkbox" name="<?php $my_special_features ->the_name(); ?>" value="<?php echo $item; ?>"<?php $my_special_features ->the_checkbox_state($item); ?>/> <?php echo $item; ?><br/>

    <?php endwhile; ?>

okay you have created your checkbox lists in your custom post type, now you have to display the meta results on your front end, to do that, create php function in your functions.php file

function display_special_fetures(){
    global $my_special_features; 
    $myresults = $my_special_features->the_meta();
    if(!empty($myresults)){
     foreach($myresults){
        echo '<img src="'get_stylesheet_directory()."https://wordpress.stackexchange.com/".$myresults['cb_ex'].'">';
      }
    }
}

finally place this function inside your loop or single.