*THIS IS GREAT*
I noticed on single strip comics, it takes out the background. I tried it on two different ones I have. "Welcome to Stripcreator" and "Colonel Sanders Cares". I can upload if needed.
It worked fine on three strip comics and I didn't test on two strips.
Also wanted to give you this url
http://www.html2jpg.com/
This is a tool that I am not sure if you would be interested in. The enterprise editions can convert urls to full jpgs and there may be some mass batch job or application to it that may be of use to you.
I am amazed at how clever you are to convert to png. I do not really use png usually, but it opens up fine so that is all I care about.