Which of the following is NOT a method of digital image storage?

Digital image storage methods refer to the various mediums through which images are saved and accessed in a digital format. A smartphone, while capable of storing images, is primarily considered a device that enables the taking, viewing, and sharing of images rather than a dedicated storage medium like the others listed.

Hard disks, flash drives, and tape drives are all recognized methods specifically designed for data storage. Hard disks use magnetic storage to retain data, flash drives utilize solid-state storage technology, and tape drives employ magnetic tape for storage purposes, often used for backups and archival. On the other hand, a smartphone's primary function is as a communication and computing device, which contains these storage methods internally but does not serve as a standalone image storage solution. Therefore, among the options, the smartphone does not qualify as a conventional method of digital image storage in the way that the others do.