"Why didn’t you use the other side of that island? To the left. It would have changed the line of sight by about 20 degrees to the north."
You've never shot a bearing have you? Done any land nav? I'm not trying to be facetious here. I'm just trying to figure out how to explain to you how to plot a line of sight. Imagine the picture below is a window and you have a laser pointer. If I asked you to stand at the center of that window and point the laser at the contrail, what would the laser light cross over on its way to the contrail? Certainly not the other side of the island. A photo is like looking through the scope of a gun. The center of the photo is the bullseye you are aiming at. You are on the other side of the camera, looking at that bullseye. So point your laser through the view of the camera at the contrail in the background, and figure out what geographic references you could use to depict the resulting line of sight from you to the contrail. Once you've got those references, plot them on a map (or Google Earth) and you have a line that depicts your line of sight to whatever it is you're looking at. With two lines of sight, you can figure out if the object you are looking at from two different locations is the same object. 
You've never shot a bearing have you?Not from a still pic with no compass references, no.
Done any land nav?
Lots. But only by my own sense of direction and topography. I have spent hundreds of hours alone in the wilderness and never have lost my way although I rarely take out my compass.
If I asked you to stand at the center of that window and point the laser at the contrail, what would the laser light cross over on its way to the contrail?
That was my point in asking why you didn't use the other side of the island. The starting point you used was right of center. But it's a photograph anyway so the landmarks you cross would not be the same as they would if you were actually there shooting a laser line across the landscape. Foreshortening in the foreground of the photo changes the relative size of objects in terms of distance (or length as you measure from near to far). If you had a photo taken from directly above the landscape you could get a fairly accurate line if you had two identified points.