Bobby Brown -- I'm Gonna Nail Whoever Took Deathbed Pic of My Daughter

Bobby Brown is on a mission to expose the person responsible for taking a photo of Bobbi Kristina in hospice.

We got Bobby at LAX and asked if he agreed with his sister's rage-filled rant about the photo -- and he made it clear ... the Brown family's standing together on this.

As we first reported ... someone is actually shopping the pic around to websites and magazines.