How to view high-res images in iPad 3 without downsampling?
There are a handful of workarounds for saving images without being downsampled, use what works for you:


Tap and hold the image to save it to Photos app as high resolution, despite being downsampled in Safari
Save the image to iPhoto
When publishing images, use PNG or progressive JPG
Email images to the iPad


This is a well documented quirk in Safari on the retina iPad, it could be a bug or just a way to make the web browsing experience more fluid given current limitations of hardware. Who knows, but it’s easy to get around for now.

Source: OSXDaily

You can also report issue to Apple.