How to stop automatic image resizing

As you know, when you choose the “linked to page” option for an image, it will open in a new page. My problem with this is the image is automatically resized by 50%; e.g. a 400px wide image will be reduced to 200px wide when someone clicks on the thumbnail and the larger image opens.

How do I stop this automatic resizing? I want the image to open in a new page at its full size.

You can see what I’m saying if you click on one of the thumbnails here:

http://www.celebslam.com/lunch-with-ali-larter

Thanks