User blog comment:SatoTheDancer101/Dance Quest Championship - Episode 4/@comment-31000046-20170105204319

"How do I prove that I completed the challenge?"

Since you'll be playing as P2 in Oishii Oishii and P3 in PoPiPo for the Mini Challenge, if you use a smartphone to take pictures of your score, you can press and hold your finger on your screen to take multiple images. So all you have to do is start taking multiple pictures right before pressing "DANCE NOW" or pressing "A" or "X" or whatever to start a dance.

Another way of proving that you did a Mini Challenge is to make a video. Make a video of you selecting a coach, starting a dance and upload the video unlisted to YouTube or upload the video to mega.nz. This may seem troublesome, but this is for proof, after all.