Yoren Chang

Thanks to <a href="https://github.com/WebDevStudios/Taxonomy_Single_Term" rel="nofollow ugc">Taxonomy_Single_Term</a>, a library created by <a href="http://webdevstudios.com/" rel="nofollow ugc">WebDevStudios</a>, it made my work much easier on creating this plugin.
With Categories Metabox Enhanced, you can:
<ul>
<li>Change the built-in Categories metabox/panel to a single term UI, which means replacing the checkboxes with radio buttons or a select drop-down.</li>
<li>Apply the single term UI to other hierarchical taxonomies in the plugin’s Settings page.</li>
<li>Customized the single term UI by setting these options:
<ul>
<li>Priority and position of the metabox placement.</li>
<li>Title of the metabox.</li>
<li>If child-terms should be indenting.</li>
<li>If adding of new terms from the metabox is enable.</li>
</ul>
</li>
</ul>

Categories Metabox Enhanced

Replace the checkboxes with radio buttons or a select drop-down in the built-in Categories metabox and Gutenberg sidebar panel.

Willy Bahuaud

This plugin add a metabox which allox to upload and link multiple images to one post. 
Pictures are linked by the way of meta_value (and attachments ID). They can be reordered using drag and drop.
Number of allowed pictures and concerned post types can be overited using hooks.
Plugin includes many functions to retrieve linked pictures. 
For more information on using the plugin, refer to the section <a href="/extend/plugins/multi-image-metabox/other_notes/" rel="nofollow ugc">“Other Notes”</a>.
<h3>Set concerned post types</h3>
Paste this into your theme’s functions.php file :
 
<h3>Set allowed number of picts</h3>
Paste this into your theme’s functions.php file : 
 ‘_image1’, 
 ‘image2’ => ‘_image2’, 
 ); 
 return $picts; 
 } 
 ?>
<h4>Set allowed number of picts, depending to the post_type</h4>
Paste this into your theme’s functions.php file : 
 add_filter(‘list_images’,’my_list_images’,10,2); 
 function my_list_images($list_images, $cpt){ 
 global $typenow; 
 if($typenow == “my_custom_post_type” || $cpt == “my_custom_post_type”) 
 $picts = array( 
 ‘image1’ => ‘_image1’, 
 ‘image2’ => ‘_image2’, 
 ‘image3’ => ‘_image3’, 
 ); 
 else 
 $picts = array( 
 ‘image1’ => ‘_image1’, 
 ‘image2’ => ‘_image2’, 
 ‘image3’ => ‘_image3’, 
 ‘image4’ => ‘_image4’, 
 ‘image5’ => ‘_image5’, 
 ‘image6’ => ‘_image6’, 
 ‘image7’ => ‘_image7’, 
 ‘image8’ => ‘_image8’, 
 ); 
 return $picts; 
 }
<h3>get_images_ids()</h3>
This function have to be used into a template file, or any function. 
It return an array of the linked attachments’s ID.
It take two arguments whose are :
<ol>
<li>include the thumbnail ? (boolean) if true include the thumbnail in the returned datas</li>
<li>
ID (integer) for targeting images linked to a specific post
 45, 
 ‘image1’ => 5, 
 ‘image2’ => 6, 
 ‘image3’ => 12, 
 ‘image6’ => 20, 
 ‘image7’ => 15 
);
//Empty pictures ar not returned
?>
<h3>get_images_src()</h3>
This function have to be used into a template file, or any function. 
It return an array of URIs and dimension for the linked attachments’s, by order.
</li>
</ol>
It take three agruments whose are :
<ol>
<li>size (string) the size to return</li>
<li>include the thumbnail ? (boolean) if true include the thumbnail in the returned datas</li>
<li>
ID (integer) for targeting images linked to a specific post
 array( 
 [0] => ‘http://url_of_the_medium_pict.jpg’, 
 [1] => 340, 
 [2] => 200, 
 [3] => false //I’ve no idea what is it… 
 ), 
 ‘image2’ => array( 
 [0] => ‘http://url_of_the_medium_second_pict.jpg’, 
 [1] => 340, 
 [2] => 200, 
 [3] => false //I’ve no idea what is it… 
 ) 
);
?>
<h3>get_multi_images_src()</h3>
Same as get_image_src(), but return two sizes for all the pictures.
</li>
</ol>
It take for agruments whose are :
<ol>
<li>size (string) the size to return</li>
<li>size2 (string) another size to return</li>
<li>include the thumbnail ? (boolean) if true include the thumbnail in the returned datas</li>
<li>
ID (integer) for targeting images linked to a specific post
 array( 
 [0] => array( 
 [0] => ‘http://url_of_the_medium_pict.jpg’, 
 [1] => 340, 
 [2] => 200, 
 [3] => false //I’ve no idea what is it… 
 ), 
 [1] => array( 
 [0] => ‘http://url_of_the_full_pict.jpg’, 
 [1] => 1020, 
 [2] => 600, 
 [3] => false //I’ve no idea what is it… 
 ), 
 ), 
 ‘image2’ => array( 
 [0] => array( 
 [0] => ‘http://url_of_the_medium_second_pict.jpg’, 
 [1] => 340, 
 [2] => 200, 
 [3] => false //I’ve no idea what is it… 
 ), 
 [1] => array( 
 [0] => ‘http://url_of_the_second_full_pict.jpg’, 
 [1] => 1020, 
 [2] => 600, 
 [3] => false //I’ve no idea what is it… 
 ) 
 ) 
); 
//Empty pictures ar not returned
?></li>
</ol>

Multi Image Metabox

Add a multi-image metabox to your posts, pages and custom post types

Categories Metabox Enhanced vs Multi Image Metabox