Google Wallet appears to be live in the field today, based on a photograph of a payment terminal in a coffee shop in San Francisco.

The photo, captured by a GigaOm staffer, shows the Google Wallet logo on a MasterCard PayPass payment terminal. The terminal display photo also coincides with updates on the Google Wallet website, including information on the layers of security in the Google Wallet system.

Google announced in May that it was working with MasterCard, Citi and Sprint, which has the Nexus S 4G phone equipped with Near Field Communication technology on an embedded chip. MasterCard gave a sneak peek of the Google Wallet application last week to analysts and reporters in New York, where representatives said the application was within weeks of being rolled out.

Google officials have said repeatedly that the rollout would start initially in San Francisco and New York, although representatives could not be reached to discuss launch details. A MasterCard spokeswoman also said she could not confirm a Monday launch and said Google would need to provide such information.

The Google Wallet will require a user to have both a Nexus S 4G phone on the Sprint network and a MasterCard from Citi. Technology exists to allow an NFC sticker to be attached to other phones to make them capable of communicating with the PayPass terminals, but that approach is not considered as secure and it is not clear whether it will be used.

Meanwhile, TechCrunch posted a story Sunday with a photo of a notice of the various Google Wallet partners about the launch, saying it was set for Monday.

Two big concerns about NFC for a mobile wallet has been the shortage of NFC-ready phones in the US market and lack of widespread deployment of payment terminals to read signals from specific phones. MasterCard said last week there are about 150,000 retail locations with the PayPass terminals, although some officials said some of those terminals still need a software upgrade to work.

Google's website describes a range of retail partners on the project, as well as how the Google Wallet requires a user to type in a PIN to activate the application each time.