A simple tool that helps with placeholder images when building a theme.
<!-- include jQuery and the placehold lib -->
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"></script>
<script src="jquery.svg.placeholder.js"></script>
<!-- Call the plugin -->
<script type="text/javascript">
$(function(){
$('img[data-ph]').tsPlaceHold();
})
</script>
<!-- start using placeholders -->
<img data-ph="250:200" />
<!-- 3rd option is text to be written in image -->
<img data-ph="250:200:content" />