WordPress by default adds an extra 10px to the width of the container that wraps images with captions. This is because the default styling for captions has a thin border that surrounds the entire image.
In a recent design I decided I wanted to caption images in a slightly different way and just have the caption below the image without the surrounding border like so.

Its a cat!
To remove the additional 10px just add the following code to your function.php
.
function remove_caption_extra_width($width) { return $width - 10; } add_filter('img_caption_shortcode_width', 'remove_caption_extra_width');
Nice touch here Matt.
Styling WP Captions is like walking barefoot over Lego – especially in a fluid environment – this will be helpful to many I’m sure! 😀
Yeah, I agree, that’s a nice clean look for captions… will definitely save this code snippet.