This is very well possible; I do this by exploiting the SVG to image converter from Highcharts. You simply find the svg code in the page and POST that to the highcharts exporting server along with a type paramater (e.g. image/jpeg), as width, and the filename to save it as.
Only downside: IE is not rendering SVG but VML for Google visualizations. No solution there yet, but it seems Highcharts also have difficulties with IE and VML to SVG conversions. So no luck there I'm afraid.
<form method="post" action="http://export.highcharts.com/" id="imageGetForm">
<input type="hidden" name="filename" value="savedFromGoogleVisualization" />
<input type="hidden" name="type" id="imageGetFormTYPE" value="" />
<input type="hidden" name="width" value="900" />
<input type="hidden" name="svg" value="" id="imageGetFormSVG" />
</form>
and execute the following script:
var svg=document.getElementById('chart_div').getElementsByTagName('svg')[0].parentNode.innerHTML;
$('#imageGetFormTYPE').val('image/jpeg');//e.g. image/jpeg application/pdf etc
$('#imageGetFormSVG').val(svg);
$('#imageGetForm').submit();
Working example here: http://jsfiddle.net/P6XXM/