Larger images and blurry images in IE

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How/where do you change the setting so that the thumbnails are the only way of viewing the images? currently i have thumbs and then the user can click on each thumbnail and it makes the image larger. i do not want this feature, just thumbnail viewing sizes.

my thumbnails are blurry and muddy looking but when clicked on to view larger (which i don't want) they are very sharp and clear? Is this a pixel size setting or something in the config wizard? Thanks!