Plenty of evidence.
Here is the photo again of Ron Paul with his friend and supporter, the former KKK grand wizard Don Black:
Doesn't look photo shopped to me.
Also, as evidence that the professional politician (who ran a racist newsletter and opposed the civil rights act) knew the former KKK grand wizard, here is a NYTimes article which claims that he was implicated by a lawyer in a trial in which the former kkk grand wizard was a defendant.
http://www.nytimes.com/1981/06/14/us/judge-denies-connally-subpoena-in-trial-of-3-alleged-mercenaries.html
Court trials are a matter of public record and I doubt that such a periodical as the New York Times would fabricate such a claim. In case you're dumber than I thought, just because the judge rejected the subpoena does not mean that a professional politician who runs a racist newsletter would not have been aware that he was implicated.
Laughing at a lack of evidence that he knew who Don Black is the same as calling him stupid, and I don't think he is stupid.
Then there is the fact that Don Black made a campaign contribution and Ron Paul publicly refused to give it back.