The ticket will have a QR code that they can scan, like what you can do at airports now.
http://ei.marketwatch.com/Multimedia/2012/10/09/Photos/MG/MW-AV111_smmlb1_20121009132119_MG.jpg?uuid=c5bc1d1c-1235-11e2-b403-002128049ad6
Not sure if posted already. Chapman being Chapman: http://m.mlb.com/video/topic/28033182/v34891097/aricin-chapman-fans-side-using-103104-mph-pitches/?cid=as_mlb_20140729_28667256