For a project I needed to work out a way to make thumbnails/screenshots of HTML files for some Java code I was working on. From my research, I found a nice project called the The Flying Saucer Project which has an XML/XHTML/CSS 2.1 renderer which works for what I needed for my project. Taking the HTML files and using JTidy to make them in to XHTML the renderer could output an image file for me.