From the looks of your image I assume that you want it to be fixed to the bottom.
To do that place your image view in the bottom of its superview and change the autosizing to be fixed to the bottom like in this image below.
The little red box in the view labeled "example" shows you how the image view will behave when the superview is resized.

If you want your image view to have a constant position anywhere else, just position it where you want it and set the appropriate autosizing for it (once again, look at the red box to see how it will behave when resized).
If the right pane is not visible press the right pane button in the tool bar (image below) or use the keyboard shortcut ⌘</kbd>+⎇</kbd>+0 to display the right pane or ⌘</kbd>+⎇</kbd>+5 to go directly to the size inspector.
