Big whoop. The hash collisions of MD5 allows an "attacker" to prevent himself from posting his own image. A simpler and cheaper way to perform the same "attack" would be to just not post the image in the first place as the outcome is the same.
When action is taken on the first image, the collided image could also be censored.
That being said, you could probably create a pair of colliding images, give one to a news outlet or something, then later post the second (presumably banned) one. The app would on short notice need to decide between banning neither or banning both.
Yeah they did this - except the contraband was automatically recognised and both images were banned via hash.