Last Sunday Disneyland Resort got rid of the hand stamp used to get back into the park. From now on they'll be taking a photo of everyone with an admission ticket before they go into the theme park.
Photos will be required for everyone with multi-day tickets and one-day tickets. Since annual pass holders already have a photo, they won't need to re-take one. With the photo, when a guest wants to return to the park, cast members just need to scan your ticket and your photo will appear on a computer screen for verification.
Similar techniques are already being used at other theme parks. Walt Disney World in Florida uses your scanned thumbprint to re-enter their park (via OC Register).