If an application needs to share Photos and Video to an iOS device, it needs to store the files in the Photos album of your device in order to work. On an Apple device, the permissions will be granular. If you want to send a picture through an app like Facebook Messenger, you will get a pop-up asking for your permission to access your device's photos. That is normal, so don't freak out. If an app is asking for permissions to certain areas of your iOS device (like Contacts, Location, etc.) that don't seem to relate to the app's function, be wary. If you want to alter your permissions, go to "Settings", then tap the app relevant to your concerns, and switch the permissions on/off.