Iconic is a simple Mac program that provides you with a quick way to change the icons of your folders. The application comes with easy to configure settings, supports many image formats and drag-and-drop actions, and immediately applies the folder icon changes.
All you need to do is to drag-and-drop the image and folder over the indicated areas and the utility will do the rest. You can preview the folder icon before importing the directory in question. Once the folder is imported, its icon is automatically updated.
Unfortunately, the application doesn't always provide you with quality results. To be more precise, the program occasionally fails to generate an icon that looks like the original picture, especially when importing color photos. Even though in the "What's New" section from its homepage it says that "The color of the icons is no longer slightly washed out.", this isn't actually true. I tested 3 different images, color and black and white, and the app didn't match my expectations.
Furthermore, if you want to undo the folder icon change you need to restart the app and drag-and-drop the directory. Also, a built-in help guide wouldn't hurt as I had to figure out myself how to change folder icons and undo changes.
With that being said, you should look for a different Mac tool for changing folder icons.