It would seem it is not currently possible to upload a PNG image from local file system:

![enter image description here][1]

This happens when I try to upload just any PNG. I [just had to][2] first upload to imageshack and then upload to Stackoverflow via "From the web."

Despite I am using IE8 I don't believe this to be browser-related, for I can upload gifs and jpegs no problem.

  [1]: https://i.sstatic.net/67i19.gif
[2]: http://stackoverflow.com/questions/17135679/find-cell-location-if-blank/17135887#comment24800004_17135887