janemig on "Responsive images get blurry when reduced"

Hi!

Trying to troubleshoot why my images get blurry on my responsive Wordpress site when they gets reduced (when you narrow the screen). I tried using png24 files and it still happens.

Here is my site: http://test.bellabellies.com/blog/. The "Blog!.." header image looks sharp at 100%, but gets fuzzy and blurry when reduced.

Any clues why?

Many thanks!
Jane