Instructions apply to most iPhones and modern digital cameras.
Use the Cloud or Wi-Fi
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The most effective solution relies on wireless networking technology.
Most modern professional or prosumer cameras now feature Wi-Fi or Bluetooth radios.

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Just plug a USB cable into your camera and connect it to this special machine.
Then, plug this adapter into the Lightning port on your iPhone.
The Photos app on your iPhone then launches.

image credit: Apple Inc.
Tap theImportbutton to transfer the photos.
Tap eitherImport Allor opt for individual photos you want and tapImport.
You’ll have to installNikon’s Wireless Mobile Utility appto transfer the images.

image credit: Apple Inc.
Canon offers a similar rig: the SD-card-style W-E1 Wi-Fi Adapter.
Other wireless adapters and SD cards are also available.
One popular choice is the Leef iAccess reader.

image credit: Nikon
Depending on the accessory, you may need to install an app.
The Leef unit requires itsMobileMemoryapp, for instance.
If it is, then unplug the adapter, wait about 30 seconds, and plug it in again.

image credit: Leef
Unplug the camera or SD card, wait about 30 seconds, and take another crack.