I think there's a little ambiguity in the question: a frame must be specified in a coordinate system. But I think you're looking for a rect relative to the original, unclipped image.
If that's right, then the rect can be computed as follows. Say the image is called image
, and the image view is imageView
. The size of the rect is the size of the image view:
imageView.bounds.size
And, since aspect fill will center the oversized dimension, it's origin is:
CGPointMake((image.size.width - imageView.bounds.size.width) / 2.0, 0.0);