Here's just another Knuckles stamp. I have no clue what the source is from, but it looked cool.
It is part of a group of two shots with 3 characters in each.
EDIT: It's from Sonic Chronicles (I would have never guessed that. Why isn't the game this cool?)
Here's the other Characters in this set:
Knuckles the Echidna is property of (C) and Sonic Team