create one UIImage from two UIImageView.

Get the two underlying UIImages. Create a new UIImage the size that you want the resulting image to be. Lock focus on that new image. Draw the first image. Draw the second image. Unlock focus.

And no, I'm not going to provide code: that should be more than enough to work it out using the documentation.

Edit: OK that's too desktop Cocoa based to work: you can't lock focus on a UIImage. Try UIGraphicsBeginImageContext(), UIGraphicsGetImageFromCurrentImageContext() and UIGraphicsEndImageContext() instead.