I just managed to constrain the image by setting only one dimension of the image - at 120% of the div, and not showing overflow.
Seems to solve this part of the problem, unless there's a reason this is a bad way to do it?
I did it like this:
Code:
<div class="square one" style="overflow:hidden;">
<div id="square_caption1" class="square_captions">The Nest</div>
<div id="cf" style="overflow:hidden;">
<img class="bottom" style="width:120%;" src="images/the_nest_residences_1_color.jpg">
<img class="top" style="width:120%;" src="images/the_nest_residences_1.jpg">
</div>
</div>