>>21221992 pb if correct and it's an overlay then it is visual confirmation of correct bullet speed.

Here is his setup. And explanation. He says there was only one frame.

https://www.techradar.com/cameras/one-in-a-million-pro-photographer-reveals-how-he-took-the-president-trump-flying-bullet-photo-with-a-sony-a1

(Portion of the article). As Mills explained: "I just happened to have my finger on the shutter and I heard the pops and just kept shooting. I didn't know what I'd captured, but when I got to my laptop, I can see that bullet flying behind his head, because it's definitely not in the frames right before it and it's not in afterwards – it's only that one frame. I was shooting at 1/8000s – it captured that streak behind him".

Anticipation and preparation are a key component of being a pro press photographer, as Mills added: "I've covered the President for 40-plus years and I always know which way they come on stage and which way they go off. The closest stairs were over to my right, so I ran over there and witnessed him being helped up to his feet".