[sebzim4500]

They could still do the scanning, but if the photo fails it would just refuse to upload it and display an error to inform the user that the photo will not synchronize. There is no reason that the results of the scans need to be sent to Apple servers.

[nicce]

If you read the technical details, result of the scan is packed with the photo. So, if upload of photo fails, then result of the scan is not uploaded as well.