How to get image height to it parent [duplicate]

This question already has an answer here:

• Centering Text over Image 2 answers

I have some code:

<section class="header">
    <img src="http://ift.tt/1cDmWQh" alt=""/>
    <div class="middle-text">
        vertical-align middle centered text by image height
    </div>
</section>

I am trying to make a section which has a responsive image any height. I want it's parent have the same height.