Pictures with caption not responsive

I use a lot captions within pictures on blog & pages and just discovered that pictures with captions are not responsive because probably WordPress is adding a div with a fixed width before the image e.g.
<div class="wp-caption alignnone" style="width: 610px;" id="attachment_6644"><a class="fancybox" href="http://hive.oewf.org/oewf/oewf14/wp-content/uploads/2014/08/DSC6174.jpg"><img width="600" height="400" class="size-large wp-image-6644" alt="ÖWF Team + Kinder (c) ÖWF (Stefan Hauth)" src="http://hive.oewf.org/oewf/oewf14/wp-content/uploads/2014/08/DSC6174-600x400.jpg"></a><p class="wp-caption-text">(c) ÖWF (Stefan Hauth)</p></div>

Ist there a possibility to overwrite the style to change it into a max-width instead of width?

example from my site (still under construction)
https://hive.oewf.org/oewf/oewf14/?p=6641