How to take multiple photos with iPhone?

My brother stole my iphone 5, he's an expert using iPhone, even I have the pass code, he still takes photos without pass code (i know how: slide up from the bottom to access camera). He took 400 photos (all of them are identical). Just wonder how he did that? I have to spend lots of time to delete them (I set photo stream on automatically upload to iCloud). Any way to prevent him doing that?

Take better care of your phone and tell him to teach you to take multiple pictures and to stop taking so many identical pictures