Image click does nothing

Hi. I’ve been running a wordpress blog for over a year without major problems. One just turned up (just before the last WP update).

So far, if I inserted an image of any format in a post, the reader could click on it and then see that image in full size. Now, that click will just relaod the respective post, without leading the viewer to that image, and not offering a chance to see a larger version of it.

Does anyone know why this is?

HH