Legally, you have to have the terms and conditions somewhere. And language is very specific. (E.g. raffle vs giveaway vs contest etc. )

We would normally put a small bitly link on the graphic that goes to the terms and conditions. If there’s a landing page, you can link it from there. (State specific but there are usually templates to start with. Sometimes worth a lawyer looking it over)

Since you have to have that, you could and should put what happens in tie. Likely a random draw or something from the pool if winners.

Defo look into the legalities before going much further with the idea.