I am using NivoSlider in WordPress and implemented some responsive css to the theme, I have fixed the width & height of the images and background size in Nivo Slider also but its displaying correct size only once and afterwards its displaying big images in the slider.
Here is the link to the site : Website
Please let me know if I am missing something.
Regards
It was officially announced by nivo slider that it is responsive, Here is announcement.
http://nivo.dev7studios.com/2012/05/30/the-nivo-slider-is-responsive/
Demo :