I let a perfectly good belly get away today and I know this question gets asked a lot on this site but are there any good apps for IPhone that can take secret pictures and any tips on how to use them?

Not an app but I like to use slow mo for candids. 1080p in 120fps especially.

(January 14, 2017, 9:47 am)garadon Not an app but I like to use slow mo for candids. 1080p in 120fps especially.

would you please share more about your experience, like :
what's the pros and cons in slow mode ?
any do(s) and don't(s) ?

Slow-motion mode captures at a much faster frame rate so your videos are a lot less susceptible to motion blur. I tried it and it didn't really work for me because my phone's slow-motion mode videos are darker and don't react as quickly to changes in lighting/exposure. Your mileage may vary.

Honestly, you don't need a special app for candids, you just need to hone your technique with the camera app you have. One of these days I'll put together a thread of some candid technique tips.