When you see an image you want in Safari but don't want to follow the link (provided it's not a flash image) all you have to do is right click and select "open image in new window" or "save image to desktop". Or just click and drag the thing out into your desktop.

If it's a flash ad or otherwise something you can't do the above action on, go to Grab and make a screen shot.

Or is what you're asking far more complicated?

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