How to Make Sure a Photo Is Permanently Deleted From Your iPhone
Photos are placed on an iPhone in one of three ways: they are captured using the iPhone's "Camera" app; they are saved from the Internet using the iPhone's "Safari" app; or they are synced to the iPhone from a computer. Images captured using "Camera" or "Safari" are saved in the iPhone's "Camera Roll," while images synced with the device are saved in different folders. If you want to delete an image from your iPhone and ensure it is removed for good, you must not only delete the image from the device's memory, you must also remove it from the image folder that syncs with your iPhone.
Tap the "Photos" application icon on the iPhone's home screen, followed by the folder that contains the image you want to delete.
Tap the image you want to delete, followed by the "Trash" icon in the bottom-right corner of the image. Tap the "Delete Photo" option to delete the image.
Connect the iPhone to the computer via the USB connection cable that came with the device and launch the iTunes application.
Click the "Photos" section in the iTunes window and take note of the image folder that is synced with your iPhone.
Navigate to the image folder on your computer's hard drive and locate the photo that you no longer want to appear on your iPhone. Drag the image out of the folder and into another folder, or delete the image. Once the image is removed from the image folder that you sync with your iPhone and is deleted from the device itself, the image is completely removed from your iPhone.