The Painting (obstacle) is basically a stronger version of the Square on Strings. It has a metal square in its middle. It is found in Checkpoint 3 (Mayhem version) and Checkpoint 8. You need to use Explosive Balls Power Up to destroy it. The power up won't destroy it but it will cause severe damage to the Painting itself, if aimed properly. It is the 4th member in the String Obstacles class.