Как привязать картинки к пользователю по его id

<div id="inputsys" align="center">Добавление нового клиента</div>
    <div class="new_client_forms">
    <form id="new_client_form", action ="add_new_element.php", method = "POST" >
    <form action="<?php echo $_SERVER['REQUEST_URI']; ?>"   
    <label for = "reg_pid">ИНН клиента</label> <br />
    <input type = "text" maxlength ="10" required name ="reg_pid" id = "reg_pid" class="input-field" /> <br />
    <label for = "reg_name">Ф.И.О.</label> <br />
    <input type = "text" name ="reg_name" required id = "reg_name" class="input-field" /> <br />
    <label for = "reg_phone">Номер телефона</label> <br />
    <input type = "text" maxlength ="11" required name = "reg_phone" id = "reg_phone" class="input-field" /> <br />
    <label for = "reg_credit">Сумма кредита</label> <br />
    <input type = "text" name = "reg_credit" required id = "reg_credit" class="input-field" /> 
    <br /> 
    </div>
    <input type = "submit" id = "submit" name = "submit" class="button-send" value="Отправить" />

<div class="Upload file" align="center" >
    <form enctype="multipart/form-data", method = "POST" >
    <p><input type="file"  name="photo" multiple accept="image/*,image/jpeg" >
    <input type="submit" value="Upload file"></p>
    </form>
    </div>