Well, you can always do imageView.layer.contents=nil;
, but I am not sure that this is exactly what you need.
This is the modified version from the comments below:
Use UIGraphicsBeginImageContext()
to create image context. You can draw UIImageView by calling -drawInRect: method, and then you should create path, that will contain areas you want to "erase", and set CGContextSetBlendMode(context, kCGBlendModeClear). Stroke the path after that, and capture the resulting image by calling UIGraphicsGetImageFromCurrentImageContext(). Then just call UIGraphicsEndImageContext() to clean up.