Upvote:4
Valid tickets have either a booking reference (PNR) or a ticket number or both. That is a unique identifier. If there is one on there, you can almost always check the booking on the airline's website or give them a call.
If there is no PNR or ticket number, than it's not really a ticket. Could be a receipt, or an itinerary, or a fake. However, you couldn't use it to check in.