I downloaded an image from flickr which is 2800 X 2100 but when I upload and put it on my website it appears small (about 500 wide). I tried changing the width attribute but it can only become smaller not bigger. My page width is about 800 and the image is no where near that size. Why? Below it the link to the image.
I think you can try to edit the images in Photoshop.
Apart from that also check your page settings attributes as well.
If that still did not work than try to run your page using firefox and try to debug using firebug.
Hopefully it can fix your problem.