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You can add your own Twist and Yes certainly photos are okay.

However video is recommended

I mean literally ‘how to share it’ link or copy/paste or what...?

You have to make a Tweet

Seven77 Challenge Tweet
Step 1. Write One reason why you believe in STEEM
Step 2. Write Day X of #Seven77 #STEEM @nathanmars7
Step 3. Attach video of you doing Seven e.g. push-ups

Please do not include any links with Seven77 Tweet

Example Tweet and If you go to my pinned Tweet you'll see many Examples from our fellow STEEMians

Hope it makes sense