1)How about if you just mark the center of the image with a white "x" or something like that? I like to move the image center by dragging the overlay around, but it might help to have the center of the image marked, it can get kind of busy looking with multiple overlays and your corner markers are super.
2)or a separate tool = "centroid" where you click the toolbar, image overlay shows some markings to let you know the tool is on, and while in the tool you can use the arrow keys to nudge the center around?
1)How about if you just mark the center of the image with a white "x" or something like that? I like to move the image center by dragging the overlay around, but it might help to have the center of the image marked, it can get kind of busy looking with multiple overlays and your corner markers are super.
2)or a separate tool = "centroid" where you click the toolbar, image overlay shows some markings to let you know the tool is on, and while in the tool you can use the arrow keys to nudge the center around?