Vertical alignment of images is complicated by the fact that different browsers use different baselines for the image. However, Mike Boyle at http://boyle.black-holes.org/dokuwiki_latex has an ingenious way of getting LaTeX to output the vertical offset required and puts the amount required in the filename. He uses the ideas given at http://mactextoolbox.sourceforge.net/articles/baseline.html which uses raisebox to move the image vertically.

I have used Mike Boyle's method and indeed, supplied it with LatexRender. It works well. Again though remember it won't be perfect given the peculiarities of each browser.