I have an "Image View" horizontally and vertically centered in the container. The dimensions are 341 by 260. When run on an iPhone 6 the image is the optimal size, looks great and is proportionate to my liking for the screen size. However when run on an iPhone 4, 5, 6+ (smaller or larger screen dimensions) the image maintaines the same dimensions and is now to big or small for the screen. How do I make it scale when run on different screen sizes?
Assuming yoru using auto layout you need to configure constraints that affect the width & height of your image, as well as its center. By default if these constraints aren't specified, then autolayout will use the intrinsicContentSize of the view, which in the case of a UIImageView comes from the size of the image being displayed.
What those constraints should be will depend on exactly what you want the image to do, but a simple case may be to have leading and trailing constraints to determine the width of the view, and an aspect ratio (height=width*constant) constraint to handle the height.