[Regex conditionals?]

I'm using preg_replace for adding a text below images (my regex is here)

/<img.+?>/i

It's fine when the img is alone, it gets converted from

<img src="image.jpg" border="0" alt="" />

to:

<img src="image.jpg" border="0" alt="" /> <br /> Text added here

However sometimes the image is contained on a link

<a href="http://www.google.com/"><img src="image.jpg" border="0" alt="" /></a>

So the text in this case is placed inside the <a href, which is not what i want

<a href="http://www.google.com/"><img src="image.jpg" border="0" alt="" /> <br /> Text added here</a>

I need to achieve something like this with regexes, but i'm not sure how can i do this.

 

if(<img src="image.jpg" border="0" alt=""  />)
{
echo '<br /> Text here';
}
else if(<a href="http://www.google.com/"><img src="image.jpg" border="0" alt=""  /></a>)
{
echo '<br /> Text here';
}

Thanks for the help!