Want to use your own button/graphic for the PrintFriendly button? No problem. All you need to do is change the image source in the PrintFriendly code snippet.
First step is get your PrintFriendly button. Select your platform and copy the code snippet.
For Blogspot and Blogger
In the PrintFriendly code snippet, there's two images (one for list page, the other for post pages). Find the image tags and change the src to the URL of the graphic/button you would like to use.
Your Find the image tag and then change the src to the URL of the graphic/button you would like to use.
Custom image option is baked into the plugin. Download the PrintFriendly Plugin and activate. Then goto your plugins page and select the settings. There you can select custom image and enter the URL.