How do I position an image at the bottom of div?

Add relative positioning to the wrapping div tag, then absolutely position the image within it like this:

CSS:

.div-wrapper {
    position: relative;
    height: 300px;
    width: 300px;
}

.div-wrapper img {
    position: absolute;
    left: 0;
    bottom: 0;
}

HTML:

<div class="div-wrapper">
    <img src="https://stackoverflow.com/questions/17934332/blah.png"/>
</div>

Now the image sits at the bottom of the div.