Thank you for your interest in Aspose products. Currently converting to image is supported only in .NET version of Aspose.Words. Please see the following link for more information:
At the moment we are on final stage of synchronizing .NET and Java versions of Aspose.Words. Once we finish this work, all features, which are available in .NET version will be also available in Java version. We plan to finish this work somewhere in July. You will be notified.