Jake decided he would make himself better. Jake thought he had everything figured out. He wanted, deep down, for Luke to know what it was like to be picked on. To be the younger brother. Now Jake had given that to him. He figured Luke would come to appreciate Jake more now that he'd be the younger sibling.
Jake watched as his mother placed Luke in a playpen as Jake walked back to his room. He always wanted to be buff and tall. He was still young so he hadn't finished growing yet, but with the camera, he could speed things up. Little did Jake know that the camera of change never transformed people on what they wanted.
It would only change people based on their own random whim, or on it's dark sense of irony. So Jake changing himself was only going to turn out poorly for him. Jake aimed the old camera into a selfie taking position and hit the button. The flash over took the room as reality changed.