Note: Before reading further, be absolutely sure that you have either downloaded to your Mac or uploaded to the cloud all of the photos from your iPhone that you want to keep. Because without that step, once they are deleted, you may not be able to get them back.
When iCloud’s Photo Stream becomes a river
The best way to offload the photos you take on your iPhone is to turn on Photo Stream. However, this feature does potentially double or even triple the amount of storage that your photos takes up on your iPhone. Each photo you take will be stored in your Camera Roll as well as your Photo Stream albums. When you share that same photo in a Shared Photo Stream, you create yet another copy.
To see the total amount of storage that photos use, access the Usage option under the General section of the Settings app. Scroll down until you see Photos & Camera. Here you will see a breakdown of the amount of storage taken up by the Camera Roll, Photo Library and Photo Stream. One way to keep this duplication of photos to a minimum is to delete them from your Camera Roll after downloading them to your Mac.
Accessing the Camera Roll from your Mac
You may think that connecting your iPhone to your Mac is not necessary if you are also using Photo Stream on your Mac. Having all of your photos automatically available to you when you open iPhoto or Aperture is so convenient that you may never tether your iPhone to your Mac. Unfortunately, doing this will allow your Camera Roll to grow in size well beyond the 1,000 image limit imposed on Photo Streams.
When you do connect your iPhone to your Mac, both iPhoto and Aperture (depending on which one you’re using) will ask you if you want to delete the photos in your Camera Roll after offloading them. Additionally you can use the Image Capture app on the Mac to select the photos in the camera roll and delete them all at once. Launch Image Capture on your Mac, click on your iPhone under devices, choose “Select All” from the File menu, and press the delete button on the bottom of the window. (Prior to iOS 6, this was the only option available to delete photos from your iPhone’s Camera Roll.)
Removing all photos without your Mac
You may have already tried to use the Photos app on your iPhone to try to remove your photos from the Camera Roll. And you may have discovered that you can only select your photos one at a time — there is no “select all” option to be found. While this is a good way to selectively trim the size of your Camera Roll, there is now another way to delete all your photos.
Again access the Usage option under the General section of the Settings app and tap on Photos & Camera. This time swipe your finger across the Camera Roll item in the list to reveal a Delete button. By clicking on thus button you will remove all photos from your iPhone’s Camera Roll. This action is not reversible, so be sure you are willing to delete all photos before you tap on the Delete button.