[–] 20063359? ago (edited ago)
Images can get corrupt when being zipped. The whole zip being corrupt would be notified when you try to open the zip. That in this case would mean every image, every document inside is corrupt and you can't unzip and get the data.
But in a bunch of images, when just some of them are corrupt, the zip would usually work fine. Only these images wouldn't show when unzipped, or show nothing. So well, the problem might happen when it was zipped, or the picture was corrupt anyway before it was zipped.