After having read the stackoverflow page, JEuclid may do the job, since it looks able to generated PNG/SVG images.
If someone find a better library, please post...
However, there are some points:
1) Last version of JEuclid was published in 2010 (so it is not active anymore)
2) JEuclid uses MathML. MathML is quite verbose : is it ok for you ? (See http://jeuclid.sourceforge.net/example5.html
3) JEuclid is distributed under ASL license, which is not compatible with the default GPL license of PlantUML
(although there is a ASL version of PlantUML). We could do the same trick as for PDF export : loading the library at runtime (see http://plantuml.com/pdf
4) It would be nice is someone (you? :-) could make a snipset (simple code example) with jeuclid-minimal-3.1.9-distribution that shows how to use Jeuclide from Java code (that is transforming some XML data to PNG/SVG image).