cli to apply a custom .icns icon to any file
You can use ‘sips’ to give an image file a custom icon of itself (‘sips’ acts on the original file so it might be safer to work on a copy):
cp imagefile.jpg donorfile.jpg; sips -i donorfile.jpg
If you just wanted to give an image file a thumbnail custom icon of itself, you can stop there. Otherwise, if you have the “Developer” / “X Code” tools installed, you can use ‘DeRez’ and ‘Rez’ to manipulate the resources to copy the newly created ‘icns’ resource to a file:
/Developer/Tools/DeRez -only icns donorfile.jpg > tempicns.rsrc
Then copy the the temp file into the icns resource of the recipient file, and set the custom icon file attribute:
/Developer/Tools/Rez -append tempicns.rsrc -o recipientfile.xyz; /Developer/Tools/SetFile -a C recipientfile.xyz
Finally, restart the Finder to view the changes.
(via http://forums.macosxhints.com/showthread.php?p=372418#poststop)
