That is being inserted by WP Stats. Some image needs to be there for the counting process but not necessarily visible. Perhaps the plugin (?) has an option to not (visibly) display that image.
Or, try through Atahualpe Theme Options -> HTML/CSS Inserts -> CSS Inserts
To move it to the left, way outside the browser viewport:
HTML Code:
img#wpstats {
position: absolute;
left: -999em;
}
Or to change its size to 1 x 1 pixel
HTML Code:
img#wpstats {
width: 1px !important;
height: 1px !important;
}
After doing that check if the stats are still being processed, just to be sure, but they should.