<script language="JavaScript" src="/index/include/jquery.min.js"></script>
<script language="javascript">
    var setPreview = function(opt) {

        var inputFile = opt.inputFile.get(0);
        var img = opt.img.get(0);

        // FileReader
        if (window.FileReader) {
            // image 파일만
            if (!inputFile.files[0].type.match(/image\//)) return;

            // preview
            try {
                var reader = new FileReader();
                reader.onload = function(e) {
                    img.src = e.target.result;
                    img.style.width = opt.w + 'px';
                    img.style.height = opt.h + 'px';
                    img.style.display = '';
                }
                reader.readAsDataURL(inputFile.files[0]);
            } catch (e) {
                // exception...
            }
            // img.filters (MSIE)
        } else if (img.filters) {
            inputFile.select();
            inputFile.blur();
            var imgSrc = document.selection.createRange().text;

            img.style.width = opt.w + 'px';
            img.style.height = opt.h + 'px';
            img.style.filter = "progid:DXImageTransform.Microsoft.AlphaImageLoader(enable='true',sizingMethod='scale',src=\"" + imgSrc + "\")";
            img.style.display = '';
            // no support
        } else {
            // Safari5, ...
        }

    }

    $(function() {
        $('.img_upload').change(function() {
            var opt = {
                inputFile: $(this),
                img: $($(this).attr('img_target')),
                w: $($(this).attr('img_target')).width(),
                h: $($(this).attr('img_target')).height()
            };
            setPreview(opt);
        });
    });
</script>
<img src="" name="test_img1" id="test_img1" width="234" height="135"><br>
<input type="file" name="main_img_1" id="main_img_1" style="width:200px;border:0;font-size:12px" class="img_upload" img_target="#test_img1">
<br><br><br>
<img src="" name="test_img2" id="test_img2" width="234" height="135"><br>
<input type="file" name="main_img_2" id="main_img_2" style="width:200px;border:0;font-size:12px" class="img_upload" img_target="#test_img2">

계속 추가해서 사용해도 잘 됨..