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This will then bring up this:
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Click large and it should display the highest resolution version of that image Google can find. Sometimes it won't be able to find the image but it will offer similar images and if you repeat the process, you may end up finding the image you're looking for.
If you're using Google Chrome, you can right click on photos and then click search Google for image, it should be the 5th option down and it will offer similar results.
Looking at plenty of high res concept arts over the years, some of them aren't all that great at high res. The text will be sharp but the image is almost always made of a mixture of different images, some sharp, some not so much. Looking at the SeaWorld one for example, the people and trees are sharp but the performers and sky are blurry and have been scanned in from lower res images.
The real exception to this is if the whole image has been drawn from scratch like the Star Wars concept art or has been taken from CGI like Volcano Bay.
Hopefully this may be of some use to you.
I think
@BriMan is making the right choice to not have crazy high res images on the site. Somebody else will do it and they can pay the cost, it's not really adding anything, it can make viewing on mobile a pain and I think it's a benefit to us all to have the news coming from OU as quickly as possible.