Images can be uploaded to the STU-540 ROM using the C++ API.
Additional information can be found here: http://developer-docs.wacom.com/faqs/docs/q-stu/stu-540-modes#rom-store-reference
with additional information in: https://developer-docs.wacom.com/faqs/docs/q-sig/howto-upload-540
More information regarding STU-540/STU-541 operating modes can be found here: http://developer-docs.wacom.com/faqs/docs/q-stu/stu-540-modes