http://wpquestions.com/question/showChronoLoggedIn/id/8020

functions.php

/* showing duplicated box */
function print_duplicated_image_box( $post ) {
        wp_nonce_field( 'remove_duplicated_nonce_action', 'remove_duplicated_nonce' ); ?>
        <script type="text/javascript">
        jQuery(document).ready(function($){
                $('#scan-images-duplicated, #delete-images-duplicated').click(function(e){
                        e.preventDefault();
                        var order = $(this).hasClass('scanimages') ? 'scan' : 'delete_all',
                                p_data = {
                                        action: 'galleryduplicate',
                                        command: order,
                                        postID: $('#post_ID').val(),
                                        rd_nonce: $('#remove_duplicated_nonce').val()
                                },
                                spinner = order == 'scan' ? $('#remove-duplicated-box .spinner:eq(0)'):$('#remove-duplicated-box .spinner:eq(1)');     
                        spinner.show();
                        $.ajax({ url: ajaxurl, data: p_data,
                                success: function(content){  
                                        if(order == 'scan'){
                                                $('#duplicate-image-result').html(content).css('visibility','visible');
                                        } else {
                                                $('#duplicate-notification').html(content).css('visibility','visible');
                                                setTimeout(function(){
                                                        $('#duplicate-image-result').animate({height: 0}, 500, function(){$(this).empty().css('height','auto');});
                                                        $('#duplicate-notification').empty().css({'visibility':'hidden'});
                                                },3000)
                                        }
                                        spinner.hide();
                                }
                        });
                });
                $('body').on('click', '.delete-attachment', function(e){
                        e.preventDefault();
                        var deleted = $(this),
                                p_data = {
                                        action: 'galleryduplicate',
                                        command: 'delete',
                                        imageid: deleted.attr('id'),
                                        rd_nonce: $('#remove_duplicated_nonce').val()
                                };
                        $('#remove-duplicated-box .spinner:eq(0)').show();
                        $.ajax({ url: ajaxurl, data: p_data,
                                success: function(data){  
                                        if(data == 'success'){
                                                deleted.parent().remove();
                                        $('#remove-duplicated-box .spinner:eq(0)').hide();
                                        }
                                }
                        });
                })
        });
        </script>
        <div class="submitbox" id="remove-duplicated-box" style="padding: 10px 0 0;clear: both;border-top: 1px solid whiteSmoke;margin-top: -2px;">
                <input type="submit" class="button scanimages" id="scan-images-duplicated" value="Scan for Duplicate Images" style="float:right">
                <span class="spinner" style="display: none;"></span>
                <div id="duplicate-image-result" style="visibility: hidden; margin: 5px 0 10px; clear:both; float:left"></div>
                <div class="clear" style="border-top: 1px solid #D9D9D9; border-bottom: 1px solid #fff; margin-bottom: 20px;"></div>
                <input type="submit" class="button button-primary button-large" id="delete-images-duplicated" value="Delete Old Duplicate Images" style="float:right">
                <span class="spinner" style="display: none;"></span>
                <p id="duplicate-notification" style="visibility: hidden; height: 1em; margin: 0; padding: 5px 0; text-align: right; clear:both"></p>
        </div>
<?php
}
// add our custom box
function my_duplicated_box() {
    $posttype = array( 'individual' );
    foreach ($posttype as $type) {
        add_meta_box(
            'check_image_duplication',
            __( 'Remove Duplicate Images'),
            'print_duplicated_image_box',
            $type,
                        'side',
                        'core'
        );
    }
}
add_action( 'add_meta_boxes', 'my_duplicated_box' );
 
 
function rename_latest_file($ID, $new_name, $postID){
    $file = get_attached_file($ID);
    $path = pathinfo($file);
    $newfilename = $new_name;
    $newfile = $path['dirname']."/".$newfilename;
 
    rename($file, $newfile);    
    // update_attached_file( $ID, $newfile );
       
        $wp_filetype = wp_check_filetype(basename($newfile), null );
        $wp_upload_dir = wp_upload_dir();
        $attachment = array(
                'guid' => $wp_upload_dir['url'] . '/' . basename( $newfile ),
                'post_mime_type' => $wp_filetype['type'],
                'post_title' => preg_replace('/\.[^.]+$/', '', basename($newfile)),
                'post_content' => '',
                'post_status' => 'inherit'
        );
        $attach_id = wp_insert_attachment( $attachment, $newfile, $postID );
 
        require_once(ABSPATH . 'wp-admin/includes/image.php');
        $attach_data = wp_generate_attachment_metadata( $attach_id, $newfile );
        wp_update_attachment_metadata( $attach_id, $attach_data );
       
        wp_delete_attachment( $ID, false );
}
 
/* check image gallery duplicate function */
function check_gallery_duplication(){
        if(!wp_verify_nonce( $_GET['rd_nonce'],  'remove_duplicated_nonce_action' ))
                die;
               
        $postID = $_GET['postID'];
        $command = $_GET['command'];
       
        $imagename = $similar = $latestID = $duplicate = array();
        $attachments = get_children( array('post_parent' => $postID, 'post_type' => 'attachment', 'post_mime_type' =>'image', 'orderby' => 'post_date') );
       
        // get all filename and associative ID
        foreach($attachments as $image){
                $filename = basename(wp_get_attachment_url($image->ID));
                preg_match('/(^[a-zA-Z0-9_-]{1,})_(\d+).(jpg|png|gif)/i', $filename, $match);
                if($match[2]){
                        $imagename[$match[1]][] = array($match[2], $match[3], $image->ID, $filename);
                        $similar[$match[1]][] = $match[2];
                }
        }
       
        // return only previous image, not latest (largest number of image identifier)
        foreach($imagename as $key => $data){
                $latest = max($similar[$key]);
                foreach($data as $id){ 
                        if($key.'_'.$latest.'.'.$id[1] != $id[3])
                                $duplicate[$key.'_1.'.$id[1]][] = array( 'ID' => $id[2], 'filename' => $id[3] );
                        else
                                $latestID[$key.'_1.'.$id[1]] = $id[2];
                }
        }
       
        //Kint::dump($latestID);
       
        if($command == 'scan'){
                if(!empty($duplicate)){
                        foreach($duplicate as $key => $result){
                                echo '<p>'.$key.' <br/><strong>'.count($result).' Duplicates</strong> <a id="'.$key.'" class="delete-attachment" href="#">Delete</a></p>';
                        }
                } else {
                        echo '<p>No Duplicated Images found </p>';
                }
        } elseif($command == 'delete'){
                if(!empty($duplicate)){
                        $image_name = $_GET['imageid'];
                        foreach($duplicate[$image_name] as $image){
                                wp_delete_attachment( $image['ID'], false );
                        }
                        rename_latest_file( $latestID[$image_name], $image_name, $postID);
                        echo 'success';
                }
        } else if($command == 'delete_all'){
                foreach($duplicate as $key => $data){
                        foreach($data as $image){
                                wp_delete_attachment( $image['ID'], false );
                        }
                        rename_latest_file( $latestID[$key], $key, $postID);
                }
                echo 'Images succesfully deleted!';
        }
 
        die;
}
add_action('wp_ajax_galleryduplicate', 'check_gallery_duplication');