How to pin a URL to OS X Dock with a custom image?

1. Move/drag the shortcut to the Desktop first

2. Find an image (on the web, etc.) Open it in Preview, Select All, and Copy.

   

3. Open Get Info on your shortcut on the Desktop. Select the current icon at the top left of this window. It will highlight to be blue.

   

4. Command-V to paste the image over top of the icon.

5. Close the properties window.

6. Drag the shortcut icon to the Dock. Note that items can only be dropped between the trash can and the black divider line.

You can take it a step further too. If you have several shortcuts you would like to keep handy, create a folder. Using the same procedure as noted by in the previous answer you can change the folder's icon to anything you wish as well and then pin that to your Dock.

• Create a Folder in a location of your choice (Documents is good)
• Add your weblinks
• Change the folder's icon in the same manner as previously described.
• Drag the new folder to your Dock
• Change the Display as and View content as to your liking.

Set to Display as... Folder Otherwise you get a stack of icons... UGLY.