These images are mine.
The first is sized at 640 pixels wide and is in the image library.I used the "class=nomargins" trick and the result is that it was downsized to 550 pixels and then resized to 640. The result sucks.
The second is sized at 650 pixels and is at Flickr. I used the "class=nomargins" trick here, too, and as you can see the quality is vastly superior and the right ten pixels are cut off.
This image rocks and you may use it freely. It's a perfect pixel rule.
The third is sized at 500 pixels so you can see the whole image.