Pinterest: Pin an image from a canvas

Question

Is there a way to pin an image that is rendered on a html canvas element? I tired to send image data via base64 but Pinterest said "Error: URI Too Long" or (with smaller images) that it is not in a valid URL format.

This is my code:

    <a 
      class="pinterest" 
      href="http://pinterest.com/pin/create/button/?url=abc.xyz&media=xxx&description=This%20is%20a%20description"
    >
      Pin canvas image
    </a>

(where xxx (media) is a base64 string)

What options do I have?