Featured image on blog – blurred

Hi
I am having a problem with the featired images displayed on my blog. They just look blurred/por quality.

I have used the same images in sliders and other formats, it just seems to be when then are set as a featured image that the look bad.

See links below. One is the live blog. The other is a test page (bottom 4 images are featured images for blog posts). I can give you admin rights if that would help.

Thanks