Johnny Depp accidentally cut off his fingertip in a fit of rage ... then dipped the stump in dark blue paint and wrote on the wall in paint and blood the name "Billy Bob" -- the actor with whom Johnny accused his wife Amber Heard of cheating -- this according to Amber and her people.
TMZ has obtained this gruesome photo of Johnny's butchered finger -- WARNING ... EXTREMELY DIFFICULT TO LOOK AT. It's an exhibit in her domestic violence case against Johnny.
We're told the incident went down in March of last year, just a month after Amber and Johnny married. They were in a villa in Australia when a fierce argument erupted. According to Amber's version of events Johnny, who was drunk and high on ecstasy, smashed several bottles and windows and also slammed a plastic phone against the wall unit. She claims a piece of one of the items cut off a portion of his forefinger.