I think the stipulation was a good idea for JM. The jury will not get to see the blown-up eyeball picture at all. So all they know is that everyone agrees there was no gun or knife IN HER HAND at the second she took the photo of Travis's face.
So the jury will say, "OK, that makes sense, I mean she was probably holding the camera with both hands. But now let's look at the NEXT photo, where he's awkwardly scrunched up at the bottom of the shower and his head isn't in the photo. Now in THAT photo I bet she DID have a gun or knife in her hand and that's why this photo looks so accidental and why he's in a position indicating he's shrinking away from a weapon. And obviously the prosecutor believes that's when the gun or knife appeared or why would he only stipulate she didn't have a gun or knife for the PREVIOUS picture...."
In other words, I think the jury will interpret this as the defense trying to get Juan to agree that she had no gun or knife while taking the photos and him saying, "Oh no. I will only agree she didn't have it IN HER HAND until after she took the face photo and before she took the scrunched-up-in-the-bottom-of-the-shower photo."