They will have the privacy setting of the OneDrive folder where they are stored there.
Windows Phone creates a folder called "SkyDrive camera roll" "Camera Roll" in OneDrive where automaticaly uploaded photos go.
Depends the language you choose this folder can has another name.
By default the folder is not shared and OneDrive will warn you if you attempt ...
There is no guest account in Windows mobile. But you can use Kids corner or apps corner in Windows mobile. This will give allow someone to use your phone but only the apps you allow.
Here is what Microsoft says about Apps corner
Apps Corner lets you set up a custom Start screen on your Windows
Phone 8.1, where you can share only the apps you choose ...
i think there is no option for hide some objects and others not , BUT there is an App in the MS Store which is called "App Locker" which locks whole apps and requires an password to start them. (There are more Apps, but it'll make the point)