resize img to 50%

HTML

<div id="img_wrap">
    <img id="original_img" src="http://upload.wikimedia.org/wikipedia/en/8/81/Mdna-standard-edition-cover.jpg"/>
    <div id="rescaled_img_wrap">
        <img id="rescaled_img" src="http://upload.wikimedia.org/wikipedia/en/8/81/Mdna-standard-edition-cover.jpg"/>
    </div>
</div>

CSS

#img_wrap {
    display: inline-block;       
    position:relative;    
}
      
#rescaled_img_wrap {
    width: 50%;
}
#original_img {
    display: none;
}
#rescaled_img {
    width: 100%;
    height: 100%;
}