I wanted to try to put a fixation cross on top of images presented to avoid subject eye movements as much as possible.I am using Python's Expyriment package and thought that after present with a expyriment.stimuli.Picture I could do a present with an expyriment.stimuli.FixCross object using the clearor update input arguments. But this does not seem to work. 
Put a fixation cross on top of a image in Expyriment?
experimental psychology;software