I noticed that by using a popular js file uploader - namely uppy.js (https://uppy.io/) - image previews are blocked even though the plugin states that no elements are currently blocked on the page. Disabling the plugin gets things back to normal.
It came to my attention the last couple of days since it was working great before that.
For a live demo of the issue please try to upload an image (any image) at the examples page: https://uppy.io/examples/dashboard/.
Disable the plugin and try again.
You will notice that once Adblock Plus is disabled image previews are working again.
Since image previews are local to the browser (served from the filesystem) they shouldn't be filtered at all.
I have also filed a bug on uppy's repository: https://github.com/transloadit/uppy/issues/758