Ah, now I understand. Yes, I can zoom in and out, oddly a - sign indicating zoomed in and a + sign indicating zoomed out. However there's not a lot of difference between being zoomed in and zoomed out and I can't zoom in or out more than once (i.e. if I click on the image I zoom in, but if I click again I zoom out)!
EDIT: I'm learning! I've now found, if I left click on the photograph, the equivalent of a 'volume bar', which allows me to drag a cursor between - and + signs to achieve degrees of magnification between the two extremes. Isn't technology wonderful!