Move image(using jQuery) when user scroll the page?

I have an image:

<img title="<?php echo JText::_('AEROBOT_HELLO'); ?>" src="images/aerobot.png" id="aerobot" align="right" /&开发者_如何学JAVAgt;

And I want to move the image (make it visible any time), when user scroll the page. I tried this code:

            var $scrollingDiv = $("#aerobot");

        $(window).scroll(function(){            
            $scrollingDiv
                .stop()
                .animate({"marginTop": ($(window).scrollTop() + 30) + "px"}, "slow" );          
        });

But it's moving the whole content(which is under image) that I have on the page. So, how to move only the image with the scroll?

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make the position:absolute and adjust the top and left values:

img {z-index:1000;top:0; left:0;position:absolute;width: 300px; height: 50px; float:left;}

here is the code in example, minimize the browser for the scroll to show up

Example

to make it stay in its parent container, you have to put display:block to both of them, position:relative to the parent container. for right alignment put right:0 to the image;

img {
    z-index:1000;
    top:0;
    position:absolute;
    width: 350px;
    height: 50px; 
    background-color:blue;   
    right:0;
    display:block;
}
#parent{
    width: 400px;
    height: 400px;
    background-color:red;
    position:relative;
    display:block;
}

Example 2

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No need to use JS : use the CSS attribute position: fixed. It acts like absolute positionning, but when the user scroll, the image doesn't move up or down.