The ice dungeon has one, not sure exactly where but you need to put a block on it to open a door near the end of the dungeon, its a room you can drop down into.
Although I think I got it from the first dungeon, ah heres a screen of ones location in the first dungeon:
You know, I played the ice dungeon and the button is no place to be found, the second image you gave me must be custom because it does not exist.
You have to lift the pot first. Then if you step on the very edge of the button, it's get pressed down. Then, if you take a screenshot, you should see about half of the pressed-down button. Then you can simply copy that half, mirror it, and stick it on the other side, giving you the perfect image!