Javascript: select an image element inside a div

Question

I have a parent div gal1, inside which there can be further divs and content, but only one img element without an id as you can see below. Now I want to use only Javascript (no jQuery) to change the style of this image, using gal1 as argument (because the rest of the structure inside this div may vary, only this one image will always be there somewhere). I couldn't find any other stackoverflow question that addresses exactly my situation.

<div class="gallery-preview" id="gal1">
    <div class="gallery-preview-img" id="gal-img1">
        <img src="galleries/kevin-carls/Monks.jpg">
    </div>
    <div class="gallery-preview-text" id="gal-text1">
        <span class="gallery-name" href="">Road to India</span><br/>
        <span class="artist-name" href="">Kevin Carls</span>
    </div>
</div>

Answer 1

Than you can make use of method called getElementsByTagName('img') than you should get image and update it.

document.getElementById(gal1).getElementsByTagName('img');

Answer 2

get the content by using id, and then query images by using getElementsByTagName

function getImages(contentId) {
    var content = document.getElementById(contentId);
    // only one image, just return an item; or you can return an array
    if (content) return document.getElementsByTagName('img')[0];
}