> I really search Google before, but I didn't find
> anything exactly like I searched ... (snip) ...
> I thought someone here could give me a best answer.
In the future, just start your question with: "I tried searching the web and this forum but did not find a solution which meets my needs...(then say why the solutions you did find do not meet your needs - price is high? closed source? requires a graphical UI?)"
If you start your questions that way, it shows people you already tried the normal channels and this avoids (in my humble opinion) the somewhat rude and cryptic answers like "STFW".
I hope the OpenOffice solution (above) works for you because OpenOffice:
1. Is open source
2. Is a free download
3. After you install it (and use only the Java API access), it doesn't seem it will require a GUI.
(4. a bonus for Sun's forums - the project is supported by Sun itself)
This forum thread is now the #1 result on www.google.com for:
java ppt to jpg conversion
... and none of the other results on the first page mention OpenOffice (http://www.openoffice.org/) so I'd say you (possibly) got a better (or at least different) answer by posting here than you could through a web search.