To create a multiple image or file uploader for your website,  I would advise using Ajax and jQuery.

I found this website useful from Web Developer +

Multiple file upload forms are sometimes essential for your web application but managing upload from multiple file input boxes becomes a bit tedious and lengthy. But thanks to jQuery using which we can make this task easier too.  This tutorial will create an AJAX multiple file upload form that uses a lot lesser server side code and also provides a very nice user interface.

For the tutorial, please visit Web Developer + and make sure you are using latest version of jQuery and Ajax upload library by Andrew Valums. Grab both libraries and add them to your page header.