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Do you mean the photos you take on your iPhone are automatically uploaded and posted on your facebook ?
Please do this. Delete Facebook and redownload it from App Store. Then go to Settings > Facebook. In there, tap Settings. Turn off Photos in there. Or go to Settings > Privacy > Photos and turn off Photos there. This will prevent Facebook from accessing your photos.
Please let me know if that didn't work, so I will continue to help you
Tap and hold down the Facebook app and it will start wiggling. Tap the x button to delete it and it will be deleted. Then redownload it.
Then open Settings app. Tap Privacy. Tap Photos and disable Photos. This will prevent facebook from accessing your Photos database.
Also, if you have the Moments app from Facebook, then disable it from Settings > Privacy > Photos