It would be useful if you are able to post a zip of your .hype document and share which images are blurry, along with the OS, browser, version, and device you are viewing on.
The other item that can be a factor is if you do transformations on the item like a scale. Hype tries its best to keep good fidelity of elements, but in some cases may have to fall back on bitmap scaling methods. Sometimes you can uncheck "Use WebKit graphics acceleration" and/or "Position with CSS left/top" in the Document Inspector and get different rendering methods. Usually it is more about the image export though!