Board Thread:Support Requests - Designing Your Wiki/@comment-10658895-20130918133707/@comment-4018164-20130918145612

I would recommend opening your image directly with GIMP (or Photoshop, i'm sure they allow that too) and save your image as *.ico.

Another benifit of GIMP is that you can create an ICO image with different layer sizes, so it can match different icon resolutions (e.g. 16&times;16, 32&times;32, etc.).