Save Multiple Checkbox Values in Attachment Details

I am attempting to create a method of tagging people in the Attachment Details section of my WordPress site. Basically it creates a checkbox for each family member I have entered information for. If the person is in the photo you check the box next to their name.

I have been able to form with the checkboxes to appear next to the photos but I can’t seem to save more than one checkbox value. Every time I check a box it overwrites the old value rather than saving it as an array.

I have been trying to solve this for a while with no luck. Could anybody point out what I’m doing wrong.

This is the code from my functions file…

function attachment_checkbox_edit($form_fields, $post) {

	//get a list of all the relatives you have already entered information for
	$relatives = get_relatives_by_id();

	// get the current value of our custom field
	$current_value = get_post_meta($post->ID, "_myCheckBox", true);
	$current_value_count = count($current_value);

		$myCheckBoxHtml = "<input type='hidden' name='attachments[{$post->ID}][myCheckBox]' value='null' />";

	foreach($relatives as $relative){

		// if this value is the current_value we'll mark it selected
		$checked = ($current_value == $relative['id']) ? ' checked ' : '';
	    //$checked = (in_array($relative['id'], $current_value))? ' checked ' : '';
		//$current_val_array = array_values ( $current_value );

		$myCheckBoxHtml .= "<input type='checkbox' name='attachments[{$post->ID}][myCheckBox]' id='attachments[{$post->ID}][myCheckBox]'";
		$myCheckBoxHtml .= "value='{$relative['id']}' {$checked} />";
		$myCheckBoxHtml .= "{$relative['name']} {$relative['name_last']}";
		$myCheckBoxHtml .= "</input><br/>";
	}

	$myCheckBoxHtml .= "<h1>".$attached_customs_array."</h1>";

	$form_fields["myCheckBox"]["label"] = __("Who is in this picture");
	$form_fields["myCheckBox"]["input"] = "html";
	$form_fields["myCheckBox"]["html"] = $myCheckBoxHtml;

	return $form_fields;
}
add_filter("attachment_fields_to_edit", "attachment_checkbox_edit", null, 2);

function attachment_checkbox_save($post, $attachment) {
	if( isset($attachment['myCheckBox']) ){

		update_post_meta($post['ID'], '_myCheckBox', $attachment['myCheckBox']);
	}
	return $post;
}
add_filter("attachment_fields_to_save", "attachment_checkbox_save", null, 2);

The forms look like this when output…

<td class="field">
<input type="hidden" name="attachments[75][myCheckBox]" value="null">
<input type="checkbox" name="attachments[75][myCheckBox]" id="attachments[75][myCheckBox]" value="92">Stav Levinson<br>
<input type="checkbox" name="attachments[75][myCheckBox]" id="attachments[75][myCheckBox]" value="111">Randy Levinson<br>
<input type="checkbox" name="attachments[75][myCheckBox]" id="attachments[75][myCheckBox]" value="99">Harold Levinson<br>
<input type="checkbox" name="attachments[75][myCheckBox]" id="attachments[75][myCheckBox]" value="80">Amanda Levinson<br>
</td>