I found out that Ruby's lawyer John Tonahill knew about the middle finger in the photo, and he used it to defend Ruby.
"Tonahill often used the Jackson photo to explain to visitors his belief that an epileptic seizure caused Ruby to shoot John F. Kennedy's alleged assassin. The country lawyer pointed out that Ruby pulled the trigger with his middle finger, while his other hand was thrown the opposite direction - indicative, Tonahill later told The Beaumont Enterprise, of such a seizure."
That is certainly a middle finger, not an index finger. We can see the knuckle of his index finger above it, and they are not lined up. But, why would Jack Ruby shoot with his middle finger when he had an intact right index finger? It was the index finger on his left hand that was partially amputated. I suspect what happened here is that someone provided them with wrong information. They must have thought that it was Ruby's right hand that was mutilated, and so they did it this way. But, we should start with the realization that that cannot be Jack Ruby because he had an intact right hand and surely would have fired the gun with his index finger and not his middle finger.
There is a discussion of middle finger shooting on a Smith and Wesson forum, where someone mentioned Jack Ruby shooting Oswald with his middle finger. Then, someone piped in that he had to because his right index finger was amputated after a fight. But no, it was his left. And it's part of the fingerprint record. They could only take 9 fingerprints on Jack Ruby, and the missing one was his left index finger.
And I found this on a forum:
"Ruby was missing the tip of his index finger on his left (non-dominant) hand."
Plus, there is the picture:
That's his left hand. So why, since he had an intact right hand, would Jack Ruby shoot Oswald with his right middle finger? It makes no sense, and there is no reason to think it happened. It couldn't. It wouldn't. It didn't. That is NOT him in the Jackson photo, and the whole thing is photographic lie.