I'm not sure I understand the question. Let's say you (1) displayed some picture on the screen, (2) then put some text on top of the picture and (3) now want the text to disappear again (leaving only the picture), then the solution is to simply display the picture again. E.g:
/ stimulusframes = [1=somepicture; 10=sometextoverpicture; 20=somepicture]
Regards,
~Dave