Even just 20 years ago, it took a lock pick set, leather gloves, and a black turtleneck to sneak into someone's apartment and steal their private photos and documents. This involved a ton of risk and the violation of numerous laws—forceable entry, burglary, trespassing, theft, etc.
Lazy Toms couldn't peep from the comfort of their own home—until the Internet. While it's impossible to patch all the holes of porous on-line security, here's a useful lesson in self-protection: how to keep your photos on your phone, but off the iCloud.
Stop Your iPhone From Sending Pics To The Cloud
Go to "Settings." Go to "Photos & Camera." Turn off "My Photo Stream." Also note that deleting a photo from your "Camera Roll" is different from deleting it from your "Photo Stream." If you delete a pic from your "Camera Roll" it will still be on the Cloud and your device. Delete from "Photo Stream."
Delete The Photos Already On The Cloud
Go to "Settings." Go to "iCloud." Go to "Storage & Backup." Go to "Manage Storage." Choose your phone. Turn off "Camera Roll."
Of course, this small levee doesn't protect against passcode breaches, other individuals having the pics (assuming they weren't just for your own enjoyment), Chinese government hacker gymnastics, or people taking pics of your phone over your shoulder with their phone. And if you want to have photos up on iCloud? Get two-step verification to keep them just a little bit safer.
Still, the above steps will help keep those precious megabytes (or gigabytes, you sly dog) in your possession, not someone else's.