It's not your computer. They look OK if you right click and select "View Image".
The IMG tags the have wrong values for the "height" and "width" attributes ... they should either be absent or in the same aspect ratio (if not size) as the original. 640x980 is about right for comics to display at almost original size (on a 96dpi monitor -- they always say 72 dpi but such low-res screens are rare these days). But it depends on the scan and how it was cropped, so it's best to 'maintain aspect ratio' and just resize by resolution or width.