Auto-adjust image height depending on textbox

I'm looking for a way to auto adjust an image's height depending on a textboxs size. The textbox will change in height the browser window's size (

first, the image should match the height of the textbox

As the window is resized the picture's height is adjusted

This is my html and css-code so far:

INDEX.HTML

<div class="wrapper">
    <img id="about" src="images/about.jpg">
    <div class="textbox">
        Lorem ipsum dolor sit amet....
    </div>
</div>

MAIN.CSS

.wrapper {
}

#about {
  float:right;
  padding-left: 25px;
}

.textbox {
  width: 50%;
}