Disregarding the 'free' request ...
Download and install '
GraphicConverter' (with the 'Users Manual').
---
Creating a 'Transparent' icon.
01. Either drag the web page's graphic onto 'GraphicConverter's icon ('Desktop' or 'Dock' bound), or save the web page's graphic to your Mac and then drag the graphic file onto 'GraphicConverter'.
02. Enlarge the graphic (to 300% or greater) via the popup menu at the low left of the window (you will see '100%' and a downward arrow).
03. Press 'w' (keyboard key - for the 'magic pen', also accessible via the 'Toolbox' - 'Window, Show Toolbox' menu item or 'Command K'), and click between the legs of the kitten.
04. Press and keep pressed the '<shift>' key, as you click somewhere outside the kitten. A dual selection now exists.
05. Select 'GraphicConverter's 'Edit, Make Selection Transparent' menu item.
06. Select 'GraphicConverter's 'File, Save as...' menu item. The 'Save' window will appear.
07. Press 'Command D' to set the 'Desktop' as the new files destination.
08. Make sure the 'Set Format from Extension' check box has a check mark present.
09. Click on the 'Preferences...' button. The 'Preferences' window will appear.
10. Locate 'Save' (in bold type) in the left hand list, and select 'General' under it.
11. Make sure (at least) the 'Add resource fork', and then the 'Create custom icon' check box'es have a check mark present.
12. Click the 'Preferences' window's 'OK' button.
13. Enter a new name for the new file, so as not to overwrite the original file. Just append '_01' to the existing name.
14. Click the 'Save' window's 'Save' button.
-----
Transferring the transparent icon to a folder / volume.
01. Locate and click once on the icon of the file ('nekoIR08_01.gif') created above, and select 'Finder's 'File, Get Info' menu item ('Command I').
02. Click on the upper left (small) icon, and then select 'Finder's 'Edit, Copy' menu item ('Command C').
03. Locate and click once on the (desired) folder's or hard disk drive's icon, and select 'Finder's 'File, Get Info' menu item ('Command I').
04. Click on the upper left (small) icon, and then select 'Finder's 'Edit, Paste' menu item ('Command V').
05. Close the '... info' windows.
-----
For 'Icon' creation / editing tools (commercial, shareware, freeware) visit '
VersionTracker'.