There are a few techniques available to perform this task using css. But I am going to show you the most effective one in this tutorial - this involves css position property.
I will be using this image (a cow) in this tutorial.
1. container (for both image and text)
2. image (the cow)
3. text (Moooooo...)
Here is the code
<div><img src="cow.jpg" /></div>
<div style="position: absolute; left: 20px; top: 160px;">
<span style="font-weight: bold; color: #fff;">Moooooo...</span>
Its the CSS positioning that makes it happen.