Short answer for TLDR:
On original video, I expect that Abby or part of Abby is probably in front of BG ... her image removed. Don't know how far ahead of BG Abby would be ... this is a mystery. I hope LE's experts will be able to provide good estimates of many things about BG. We'll find out at trial, likely.
I thought I'd include a bit longer explanation ... optional read, if you will:
For me these things are of curious interest BUT, I've come to understand that analyzing BG video/photo is an exercise in analyzing altered/over-manipulated enlarged pixels.
The sources of the altered material worked with LE to crop the BG image out of the original video and reassemble it on the bridge. The purpose of the images was to provide the public a reference for the BG figure - to encourage tips - about this figure (and their clothing/stature, possibly). LE has provided clothing description: blue jacket, blue jeans, hoodie hood out of jacket. Indeed, BG is the individual that appears on the bridge, captured on Libby's video moments before LE believes the abduction occurred and the "down-the-hill" can be heard on the video.
At one time these images were accompanied with height estimates for the BG figure as being 5'8 to 5'11 ... and over time the images were accompanied by two very different composites based on eye-witness accounts. Later, audio editors lifted sound, attempted to enhance, and those results were also provided to the public: "down-the-hill" and later, "guys". ISP still has the info on the girl's page:
Delphi Homicide Investigation
Youtubers with editing skills have continued to further play with, crop, enlarge, manipulate these pixels ... in an effort to support a variety of sleuther hypothesis. Well enough, but I've moved on.
(I agree that Gray's work has been helpful in giving the world a much better feel for the lay of the land and the movement and BG?/ RA? sightings of the eyewitnesses mentioned in the PCA. But that's a different contribution than further editing the BG pixels.)
Because the image has obviously been clipped, and placed back on a blurred out bridge surface with blurred background ... I tend to think the original will have one of the girls (likely Abby) in the frame, with the BG figure somewhat blocking the BG image in the background.
I landed here quite some time ago: There's a reason LE have shared the 43 second video with very few. And there's a reason they have manipulated the original image to this degree. The why of all that, I think, we will learn at trial.
BTW, to my knowledge, none of the"RA eye-witnesses" from the PCA described a hat.
Yet, one composite figure wears a hat, facial hair. Years later, another composite figure has neither hat nor facial hair. I certainly can't say if the BG figure even wears a hat, or has facial hair. But I've also I've never felt that was important. The BG image is - obviously - not a definitive ID tool on its own.
JMHO