Blurry Product Images with PC (not Mac)

Hi,
We’re facing a problem with our product images which display differently when shown on PC or MacIntosh. They appear to be blurry under PC as shown in the following page. When clicking on a product, the image in the single product page becomes neat and when coming back to the previous page, the clicked image remains neat while the other ones are blurred.
Under Mac environment, no problem at all.
I checked everything on my website, everything is updated. I tried regenerating all thumbnails, it makes no difference.
Could you help me sort this out?
Thanks for your reply

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