Google is inviting photo buffs to take part in its #PayWithAPhoto contest, in which they're giving away prizes with the help of a food truck.

The #PayWithAPhoto contest will begin on July 29 and anyone can participate in the cities where the Google Photos-promoting food truck can be found: New York City, Austin, Portland, and Los Angeles. The truck will announce an item that users must search for in their Google Photos app — and the first person to find and present a picture of that item will win a prize.

As you may have guessed, the contest prizes will be food items, since the providing party is a food truck. In other words, winning participants will be able to get truck food for free, simply by coming up with an image that meets the criteria. Participants will be able to "pay" for food with photo currency.

While the contest mechanics seem rather straightforward, there's actually more to it that Google wants users to understand. The company touts its Google Photos app as an easier way for people to save and search for photos. With the app's Visual Search feature, users can easily find a stored image by searching for the various subjects that are included in the shot — such as people, things, and places.

If a user wants to find the picture of a square pizza that he took in an old restaurant in Italy, he could search for it by entering keywords such as "Italy," "food," "square," "old," "restaurant," etc. If he remembers the date when he took the picture, he may even be able to use that to narrow down the search.

Since the contest is beginning in less than a week, would-be contestants have a couple of days to start filling their Google Photos app with pictures of everything or anything that could give them an edge. Variety will probably go a long way here.

There's no information on whether the photos should be user originals or if they can be online images that have been saved in the app. Hopefully, Google will provide more information about the contest before it begins in New York on July 29.