iCab doesn't have a free version, Opera is iPhone only. I tried three other browsers to no avail.
I found out that if you copy an image, Safari also places its URL on the pasteboard. Entering it in the URL field will get rid of the surrounding page, but still doesn't render at full size.
What does work is downloading that URL with GoodReader!
My original solution of saving the image does place the original file in the picture role, but the Photos app doesn't render at full size, either. However the threshold is higher than with Safari.
Importing from the picture roll into GoodReader also works, but is not recommended as it doesn't copy the file but the pixels, and re-saves them as JPEG. This degrades quality and increases size.
I was originally look for a way to get MSafari to snap images to 1:1 when viewing, I can't find the gesture for it and don't want to wing it by pinching.
But it looks like MSafari has other problems as well.
I see what you are saying and this is indeed disappointing.
Your image is only 600+KB, my iPhone 4 has 512 MB of RAM (more than computers of yesteryear), it's quite silly that it can't display the full res of the image and resorts to shrinking the image by 4x.
I also noticed that when you "save image", the image in Camera Roll is NOT the same as the one on the web page, it's slightly large (probably recompressed).
It seems the only way to save the image "as it is" bit for bit identical** is to use Good Reader's download protocol (where you add a 'g' to the "http://..." to get "ghttp://..."), yes it appears you need to use a 3rd party program to do something as simple as saving an image correctly ... -_-
** I compared the MD5s of the images saved from Chrome(Mac OS X), Good Reader, import from Camera Roll.