Of course you can create original artwork for .wwf on your Linux box, but wouldn't it be nice if you can use the professional artwork Matt von Jung created for this? But how do you obtain it? Very simple: use the OS/X package. First, download it. Then unzip it:
The next step is to decompress the .pax archive:
gzip -d Archive.pax.gz
This seems like a dead end, but it isn't. The .pax archive is simply a cpio file:
cpio -i < Archive.pax
cd 'SAVE AS WWF.app/Contents/Resources'
We need the .icns files. That seems like a dead end as well, but not quite. We're almost ready. If you want to extract the icons on your own machine you have to install icns2png, which can be obtained here. Installing it is pretty straight forward:
tar -xzvf libicns-0.7.1.tar.gz
It prefers you install Jasper or OpenJPEG, but I didn't have much luck with that. You don't need it either unless you want to extract the high resolution icons. After you've installed it, enter:
icns2png -x wwf.icns
Reading icns family from wwf.icns...
Saved 'is32' element to wwf_16x16x32.png.
Saved 'il32' element to wwf_32x32x32.png.
Saved 'it32' element to wwf_128x128x32.png.
Done! You can also extract the icons online. It depends on what you prefer, the result is the same.
If you need still another format, use ImageMagick better known to some as convert. Now install the icons in the appropriate directory (that depends on your desktop environment) and you're done. Enjoy!