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="blah.png"/>
</div>
Now the image sits at the bottom of the div.