inputでファイル選択後即時アップ。
[Twitter]tweet with mediaでも実装していました。jQuery.uploadを使います。
Sample ※Firefox,IE8,9で動作確認済

index.html
<!DOCTYPE html>
<html lang="ja">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<meta http-equiv="Content-Script-Type" content="text/javascript">
<meta http-equiv="Content-Style-Type" content="text/css">
<title>ファイル選択後即時アップ</title>
<meta name="description" content="****">
<meta name="keywords" content="****">
<meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes">
<link rel="apple-touch-icon" href="apple-touch-icon.png">
<link rel="stylesheet" href="style.css" type="text/css">
<script type="text/javascript" src="jquery-1.9.1.min.js"></script>
<script type="text/javascript" src="jquery.upload-1.0.2.min.js"></script>
<script type="text/javascript" src="script.js"></script>
</head>
<body>
<form method="post" action="" target="f1" enctype="multipart/form-data">
	<input id="filebox" type="file" name="image" size="0" accept="image/*"/>
</form>
<ul id="preview"></ul>
</body>
</html>


script.js

$(function(){   
	set_thumaction();
});
function remove_thum(){
	$('#preview').empty();
}
function set_thumaction(){
	$('#filebox').change(function() {
		var preview = $('#preview');
		$(this).upload('upload.php',$("form").serialize(),function(html){
			preview.append(html);
		},'html');
	});
}
function form_tweetmode(){
	$('#filebox').remove();
	$('form').attr('enctype','application/x-www-form-urlencoded');
}
function restore_form(){
	$('#fileboxwrap').html('<input id="filebox" type="file" name="image" size="0">');
	$('form').attr('enctype','multipart/form-data');
	set_thumaction();
}


upload.php
<?php
if(isset($_FILES["image"])){
	deleteFilesOfDir('./tmp');
	$html='<li>';
	$v=$_FILES["image"];
	$ext=end(explode('.', $v["name"]));
	$filename='./tmp/'.time().'.'.$ext;
	$result = @move_uploaded_file( $v["tmp_name"], $filename);
	if($result){
		$html .= '<img src="'.$filename.'" width="300"/><br/>';
	}else{
		$html .= 'エラー<br/>';
	}
	foreach($_FILES["image"] as $key => $v){
		$html .= $key.' : '.$v.'<br/>';
	}
	$html .= '</li>';
	echo $html;
}
function deleteFilesOfDir($dirPath){
	if (!isset($dirPath)) {
		return;
	}
	$res_dir = opendir($dirPath);
    while( $file_name = readdir( $res_dir ) ){
    	if (is_dir($dirPath.'/'.$file_name)) {
    		continue;
    	}
        unlink($dirPath.'/'.$file_name);
    }
    closedir($res_dir);
}
?>


jQuery.upload
http://lagoscript.org/jquery/upload