Unless something new comes to light this will be my final post on this subject. Thanks to Walls of the City I was able to get my hands on an alleged screenshot of the Brady Campaigns Facebook page with the offensive poster. I then turned to fotoforensics.com to analyze the image to see if it could be determined if it was a fake. I also grabbed a screenshot of another facebook page to serve as a control for comparison.
The analysis of the alleged Brady Campaign screenshot is here. The analysis of the control page is here. As you can see the ELA and Metadata match. Does this count as proof beyond a reasonable doubt that the image originated from the Brady Campaign? No, it does however, Brady Campaign protestations aside, provide a preponderance of evidence that the image may have originated from the Brady Campaign. Whether it did or not I leave for you to decide.