Add Custom Image Upload Meta Field WordPress.

Functions.php

<?php
/*************************************************************************/
/*                       Adding Images Meta Boxes                        */
/*************************************************************************/

add_action('add_meta_boxes', 'add_images_meta_boxes');  
function add_images_meta_boxes() {    
    // Define the images attachment for gallery  
    add_meta_box(  
        'code-gallery-attachment',  
        'Custom Attachment',  
        'code_gallery_attachment',  
        'code_gallery',  
        'side'  
    );  
      
  
}  

/********************************************************************************/
/*                            Displaying image upload Fields                    */
/********************************************************************************/
//static $i = 1;
$k = 1;
$j = 1;
$m = 1;
function code_gallery_attachment() {
	global $post;
	$i =1;
	 wp_nonce_field(plugin_basename(__FILE__), 'code_gallery_attachment_nonce');
    $html = '<p class="description">';  
    $html .= 'Upload your images here.';  
    $html .= '</p>';  
    // $html .= '<input type="hidden"  id="upload_image" name="upload_gallery_image" value="'.get_post_meta($post->ID,'code_gallery_images',true).'" size="25">'; 
    $html .= '<input type="hidden"  id="upload_image" name="upload_gallery_image" value="" size="25">'; 
    $html .=' <input id="upload_image_button" class="button" type="button" value="Upload Image" />' ;
    echo $html;
    $gallery_images = get_post_meta($post->ID,'code_gallery_images');
    ?>
    <?php if(  sizeof($gallery_images) > 0  ){?>
    <div id="togglediv">
    <?php if($gallery_images[0]!= NULL){foreach ($gallery_images[0] as $key=>$value ) {
    	if($value != NULL){?>
    	<input class="images" type="text" id="firstimage<?php echo $i?>" name="code_gallery_attachment[]"value="<?php echo $value;?>" />
    	<div class="editthumb" id="imagediv<?php echo $i;?>">
    		<img src="<?php echo $value;?>"><span class="removebtn"><a id="removebutton<?php echo $k++;?>" onClick="removeImage(<?php echo $i;?>)"class="glyphicon glyphicon-remove buttonremove" ></a></span>
    	</div>
		
    	
    	<?php $i++; } ?>
    <?php }}?>
    
	</div>
	<?php }?>
	<script type="text/javascript">
		function removeImage(id) {
			console.log(id);
			if(!id)
				id = "";
			jQuery('#firstimage'+(id)).remove();
			jQuery('#imagediv'+(id)).remove();
		
	}
	</script>

<?php }


/**********************************************************************************/
/*                              Save the Metabox Data                             */
/**********************************************************************************/

add_action('save_post', 'code_save_images_meta', 1, 2); // save the custom fields
function code_save_images_meta($post_id, $post) {
	// verify this came from the our screen and with proper authorization,
	//because save_post can be triggered at other times
	 // if ( !wp_verify_nonce( $_POST['jit_gallery_attachment'], plugin_basename(__FILE__) )) {
	 // return $post->ID;
	 // }
	// Is the user allowed to edit the post or page?
	if ( !current_user_can( 'edit_post', $post->ID ))
		return $post->ID;
	// OK, we're authenticated: we need to find and save the data
	// We'll put it into an array to make it easier to loop though.
	if( isset( $_POST['code_gallery_attachment']) ) :
		$gallery_meta['images'] = $_POST['code_gallery_attachment'];
	// Add values of $gallery_meta as custom fields
	foreach ($gallery_meta as $key => $value) { // Cycle through the $gallery_meta array!
		if( $post->post_type == 'revision' ) return; // Don't store custom data twice
		$value = implode(',', (array)$value); // If $value is an array, make it a CSV (unlikely)
		if(get_post_meta($post->ID, $key, FALSE)) { // If the custom field already has a value
			update_post_meta($post->ID, $key, $value);
		} else { // If the custom field doesn't have a value
			add_post_meta($post->ID, $key, $value);
		}
		if(!$value) delete_post_meta($post->ID, $key); // Delete if blank
	}
	
	update_post_meta($post->ID,'code_gallery_images',$_POST['code_gallery_attachment']);
	endif; //isset End
}