UIImageJPEGRepresentation has been replaced by instance method UIImage.jpegData(compressionQuality:)

The error is telling you that as of iOS 12 the old UIImageJPEGRepresentation function has been replaced with the new jpegData method on UIImage.

Change:

let imageData = UIImageJPEGRepresentation(image, 0.75)

to:

let imageData = image.jpegData(compressionQuality: 0.75)

Similarly, the use of UIImagePNGRepresentation has been replaced with pngData().