How do you require a passcode to take photos?

Yes, you can set a restriction.

Settings > Screen Time > Content and Privacy Restrictions > Allowed Apps > Camera: OFF

Note you need to enable Content and Privacy Restrictions to make changes,

best you also use Screen Time Passcode so it cannot be change without the passcode.

Note: Should you forgot the restrictions passcode,

you can only restore your iPhone as new, clearing all data from your iPhone.

If they deleted your photos your iPhone had to be unlocked. Set a passcode on it.

An iPhone can be used to take photos when locked. This is convenient as it allows you to take photos quickly without having to first unlock the phone. However, the photos it takes while locked are the only photos accessible when the phone is locked, and only then until the phone goes to sleep. Once the screen turns off those photos are no longer accessible. It is not possible to view any other photos on the phone or to delete them unless the phone is unlocked. So if someone deleted photos from your phone it must have been unlocked.

Find My iPhone Activation Lock - Apple Support

Read my previous post.

Try it, you got nothing to lose.

You're welcome.