Aggressive image blurring
Updated to not blur the captcha image.
Copy below code Options > Theme > Paste > Save
img { filter: blur(10px);}
img:hover { filter: blur(3px);}
img.full-image { filter: blur(0px);}
div#captcha_objects img { filter: blur(0px);}
Note: Use incognito, blurred images are still downloaded. Dump your browser cache.