As I'm sure you know, Shelley is the most "witnessed" person on the TSBD steps around the time of the assassination and places himself " Just outside the glass doors there.", as seen in Altgens 6.
This is the picture he was shown from "Four Dark Days in History":

He confirms he was stood next to Lovelady at the time but is there any real mystery as to why he couldn't ID himself in the picture?

No, there is no mystery whatsoever: Mr Shelley knows where he was standing in relation to Mr Lovelady--------west of him--------and that's how he knows he was not
in view of the camera.
If he had been standing where you------------in your desperate
Doylesque effort to magic him into Mr Molina so you can magic Ms Stanton into Prayer Man--------------think you see him in Altgens, he would not be stating categorically that he was not in view of the camera.
Here's where Mr Frazier places Mr Shelley in his WC testimony: "standing, you know, back from the top step and
over toward the side of the wall there". And before you throw more nonsense at us by suggesting Mr Frazier might mean the east wall, he makes it clear he means
the same wall Mr Lovelady was nearest to.
Here's what Mr Shelley himself says, in the March 64 document you love cherry-picking quotes from, about Mr Lovelady's position in relation to him: "seated on the entrance steps just in front of me". This, again, places Mr Shelley unequivocally on the west side of the entranceway. Whereas your Shelley-in-Altgens is on the east side. (So... you have transposed Ms Stanton from east to west and Mr Shelley from west to east. A classic double
Doyle maneuver!)
Furthermore! Mr Lovelady-----------who, like Mr Shelley-----------will have seen the Altgens photograph many times by Jan 64, and who was very soon after the assassination shown an FBI blow-up of it, never once indicates that he can see, or thinks he can see, Mr Shelley in the photograph. He only mentions the
lady shielding her eyes who works on the second floor. Again, the simple reason is: he, like Mr Shelley, knows that Mr Shelley is not in view of the camera.
Again I challenge you:
show us the lady shielding her eyes who works on the second floor you think Mr Lovelady means!