Saving HTML 5 Canvas Into A File That User Can Download.
Using Client And Server Scripting

The image below consists of randomly generated circles drawn on HTML 5 canvas object.
You can press the Save button to save the image. It will then prompt you to dowload the image.
Reference:
http://www.permadi.com/blog/2010/10/html5-saving-canvas-image-data-using-php-and-ajax/

Wait for a while after clicking the button and the browser download should prompt you to save the file.