When members place an order for an event ticket, and the order is updated to order status Payment Received, they are emailed a ticket for the event. That ticket contains information about the event, and a barcode.
For those that have a barcode scanner app (e.g. on their smart phone), they can scan the barcode to reveal the ticket the information.
One of our ideas for future development, is to develop a feature for event organisers to scan the ticket barcodes when people arrive at the event, which would automatically mark the member as having attended the event. However, since adding the barcodes, we haven't had much interest in the feature (and our priority list is driven by popularity), so it's on hold for now.
If you think that this would be a feature that you would use, let us know. If we hear from enough people, then we will push it to the top of the list....