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davidcyclebackAge and rarity will help determine. A tough, early Mays/Mantle postcard can have decent value, in part because many card collectors will consider it a quasi baseball card. Those team issues pictures were sold at the stadium and can have decent, if not great, value. Yours would appear to be a team/stadium issue postcard. All other qualities even (rarity, year, etc), I would think a stadium postcard might be worth more than a stadium picture print.
I'm unfamiliar with your particular postcard, so I have no knowledge of its rarity or year of issue.