Most lightbox plugins that met the responsive requirement came bundled with functionality to display videos, and transitioned from slide to slide in more elaborate ways than the next. I just wanted to popup an image.
I decided to build my own.
How to use
Requires jQuery >= 1.4 and < 3
<link rel="stylesheet" href="jquery.lightbox.css" />
<!-- Link to the image -->
<a href="myimage.jpg" data-caption="Optional caption attribute" rel="lightbox">Click me</a>