Sentence:  One could easily do this with <WSD>stereo</WSD> photographs, but one could also do it by making a pseudoscope, with a short cardboard tube and mirrors, ... 
Meaning of the word marked with <WSD> tags:  Of a pair of images: one depicting the view as would be seen from one eye and the other from the other eye, so that when viewed appropriately, they combine to give an impression of three dimensions.