http://www.nydailynews.com/news/politics/w-va-sen-rockefeller-announces-retirement-article-1.1238213
This page has such a photo (Bob Dole behind Nelson) but says it’s from a campaign stop in NY.
That's him outside his limo giving the finger to some hecklers as he entered/exited a building.
Back in the day of the '64 convention no regular news source would have carried such a photo that I recall. So it had to have been in a limited circulation conservative publication.