From a much longer interview on all things Mondo:
JS: Sometimes it's crazy. When Martin Ansin did Taxi Driver, the way we were able to get Robert DeNiro to sign off on that was, we had to send him a finished copy of the poster. So we had to take this psychotic leap of faith, finish and print the damn poster, pay the artist, and if DeNiro had said "No thank you", that would've been it. No poster.Relatedly, highlights from Jock's talk at Mondocon:
JB: That would've been over a year-long process that was just out the window.
We'd love to see Bruce Willis on a Die Hard poster, but look at what he came up with! I love that poster, it's crazy.
JB: What's funny is that on that print, we still had to get likeness approved on the building, for Nakatomi Towers. The FOX building, or whatever it is.
JB: Yeah! We sent it in (an original version) for approval and they said, "No, you can't use the building". And we were like, what?! And they said, "Yeah, you can't use the building, it's copyrighted". We were like, so we can't use Bruce Willis and we can't use the building - what sort of Die Hard poster do you think we're going to make? Luckily we were able to get with the building owners and get the thing approved. We totally cleared it.
Jock was originally brought into the film industry by Peter Berg who was in line to direct an adaptation of his comic series The Losers. Despite leaving the project, Berg remembered Jock’s talents and called on him to contribute concept work for his later films including Hancock, Battleship and Dune.
Hearing of a new Dredd film being in development, Jock put out a piece of concept art he drew on social media. Someone found access to his online directory and found 3 more pieces of art which soon spread online. He received a call from the producer of the film and instead of being in trouble found himself with an offer to work on the film.