Is it possible to write an app to behave like the photo picker does in the Photos app? Namely allowing users to select multiple images and greying out or putting a green tick on the selected ones?
I've tried UIImagePickerController, but that appears to just dim the image when it's touched.
If you’re working with iOS 4 then yes you can (but we’re bound by the oh-so-silly NDA for now), with a custom interface. Else maybe you’d like to look into Three20, it has an image picker which intend to mimic the original and works very well with custom photos (that is, not those in the camera roll or accessible with the Photos app). Maybe you could fork it and add custom behavior.