I haven't seen anyone bring this up yet ...

Finn was the most outspoken on leaving/destroying the machine even before the encounter with the dr friend who explains his death had nothing to do with "messing with time". So he knows he doesn't need to recreate the pictures. Yet afterwards, he paints the exact thing in the picture that causes Mr. B to die in the first place.

FINN KILLED MR B!

You might think his rationale (if he even thought of that) for doing so would've been "its him or me", as he paints it actually as a message to himself so that it gives him the idea of how to get the upper hand on Jasper and save his gf .....

BUT

Had he NOT painted that picture he would have accomplished something even better - Mr B never would have seen it, thought his life in danger, died, they never would have even found the camera in the first place, and life would have gone on as normal. Which - especially by that point in the film - is what the character wanted more than anything. And remember, this happened before e found out about the cheating gf.

If anything, it would have made for a more satisfying ending imo - just as he's about to paint he realizes this and stops himself ... the next scene is them hanging out as they were before ... and maybe a final scene of the camera ejecting a picture and Mr B watching it develop into some terrifying image - Finn killing Jasper and Callie (implying he found out about the cheating), followed by a close-up of Callie's face staring right into the camera (implying she survived, presumably killed Finn in doing so, somehow found out about the camera in the two-week period afterwards, and intends to use it just as she was trying to in the move), then a cut to credits.