在php中访问Javascript (jQuery)中定义的变量

在我的php文件中，javascript/html代码是使用echo编写的。我想访问的图像，将被放置在"place1"div在javascript和传递给php。

 // create a placeholder for an image- user is going to drag and drop an image here
echo "<div id= 'place1' class = 'place'></div>";
echo '<button id="apply" name="save" type="submit">Apply Changes</button>';
echo '<script src="http://code.jquery.com/jquery-1.9.1.js"></script>';
//javascipt code to find the source of that image
echo 
'<script>
    $(document).ready(function(){
        $("#apply").click(function() {
            var frame = $("#place1").children("img").attr("src");
            $.ajax({
                url: "thumbnails.php",
                type: "POST",
                data: frame
            });
        });
    });
</script>';
 // access frame variable (image source) in php ??? not sure how to do this part..
$frame = $_post['frame'];