For a relatively low cost approach, you could just have a card with a photo, name and barcode printed on it.
You'd need a barcode reader attached to a laptop on the ST turnstiles.
At the simplest level the operator could just match the name on the card to the name stored on the computer from the barcode.
People could make a card with a photo and barcode, but the barcode wouldn't match the name on the computer.
For further fraud protection, the database could spot double use to prevent cloning.
The information from the database could also be used to track each ST holders attendance, when they come and what time.
edit. Thinking about it, the database would have to be run from one computer so that the cards couldn't be passed to someone else outside the ground, and just use another turnstile. Although that would be a bit desperate.