you need to create a "Categories" folder in your skin's 'Media' dir
Name the images the same as you name the categories and they will automatically match up. The names must match.
Eg. I would create a category in Moving Pictures named "After Dark" and I would place the following image named "After Dark.png" in:
"C:\Users\All Users\Team MediaPortal\MediaPortal\skin\StreamedMP\Media\Categories\" (or wherever you've installed this dir to)
So try creating a Categories folder in your skin's Media dir and see how it goes
But if you've already done this, then perhaps there is something incompatible with the Avalon skin, or perhaps the names aren't quite matching?
Thank you for all you efforts. Right now I'm not using these images in moving pictures, but I use them as windows Folder icons.
You can convert them very simple online: http://www.convertico.com/