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When you are looking at an image search result set, the image search engine probably wants to provide images that do not look blurry when the original image source is pretty high quality. But many are and have been complaining about blurry images showing up in Google Image search.
A Google Web Search Help thread has some of those complaints that have been going on since last year!
Most recently, AJ from Google said they are finally working on a fix to the issue. AJ said:
Thanks for all of the really great feedback! We're actively working on providing a fix here, which will be coming soon. Thanks!
Here is an example from one searcher, the image on the top is the source image from Flickr and the image on the bottom is how Google shows it in the preview.
Forum discussion at Google Web Search Help.
