I would like to have one object that is always visible in the corner of the monitor, exactly at the same spot and at fixed size, no matter what the camera is tracking and what the scene is showing. How can I do this? Could parenting the camera to the object work?
It works the other way around: parent you fixed pos object to the camera,
- Select the object and place it
- Select the camera and parent Ctrl-P
You could also, depending on your screen layout, create a small 3D view area in the corner of the screen and choose View> Align View> View Lock to Active with the object you want to view, selected.
Now, whenever you move your object, that specific 3D view will always follow it:
You can also hide the header menu for that 3D view by hovering over the edge of the menu and the 3D view and dragging downwards.
If you make sure the 'Lock cameras and layers' option is unselected (it is shown as selected in the image below) in the locked 3D View you can also make it so the object will still be visible even if its layer isn't visible in the main 3D view: