There's no hidden meaning, no special motive, it was simply a comedic moment added to have fans say "Oh look, just like in MK2".
I guess johnny cage just threw the foto at him after he killed him, we don't see it? who cares, we don't see the photo slipping out of scorpion outfit either
My conclusion is that it was a set up suggestion that Scorpion is in fact a Johnny Cage super fan.
Here's why I think it:
Near the beginning of the movie Johnny Cage is filming a fight scene and the stunt guys aren't doing their stuff right. Johnny: "Where do ya get these guys?! And the press says I can't do this stuff...."
"I see the uh press is giving you a hard time"
"Yeahhhh, they think I'm a fake..."
I think, the irony, is that at some point during Shang Tsungs scouting for candidates for the Mortal Kombat tournament Scorpion was impressed with Johnny Cages fighting and even went to meet him in disguise and got that photo, choosing to carry it around with him regarding Johnny as his idol.
Something I think is worth noting is when Scorpion whisks Johnny away to the place of the second half of their fight we says "Welcome". Quite a respectful greeting to someone you're fighting to the death.
So when Scorpion goes all out and uses every trick he knows to win and still gets defeated, I think when he explodes the photo flies out from his clothes.
The fact the photo says "To my greatest fan" I took that to mean that Scorpion actually is his greatest fan and he went out the best way he could have hoped: in Mortal Kombat against his idol.