The barcode used on a mobile boarding pass is identical to the one on a paper boarding pass and can usually be used everywhere the paper version is accepted. Most commercial airlines such as United Airlines, Air Canada, American Airlines, and Qantas all support mobile boarding passes. Even Disney uses this technology to create mobile boarding passes for Rise of the Resistance and other popular rides at its Disneyland and Disney World theme parks.
Airlines and other companies that support e-tickets and digital boarding passes often send the relevant barcode to you in an email. In this case, the barcode image usually displays in the body of the email itself or in an attachment such as a PDF file.
Some barcodes included in airline emails may actually be for a receipt or proof of purchase. These cannot be used as a boarding pass.