You’ve probably set a password to access your iPhone or iPad (Settings/Passcode), and also have Auto-Lock set to kick in after so many minutes of non-use (Settings/General/Auto-Lock). This can be inconvenient when you have someone using your device to take photos (or record videos) of you while you’re speaking.
Instead of turning off Auto-Lock, do this. From the Lock screen (not the Home screen), look in the lower-right corner. You’ll see an almost transparent icon of the Camera app. Put a finger on it and flick up (not slide) to access the camera and video functions. They will not be able to access your other photos.