“Google Photos is on fire!” says a cheery David Lieb, who is standing outside a building on the company's Mountain View campus alongside every one of his fellow employees. A fire truck has just pulled into the parking lot, and an automated voice is calmly instructing everyone to evacuate. I have just arrived, and dozens of Googlers are standing around, blinking into the California sun.

Lieb, a product director for Google Photos, is not speaking literally: the building where the Photos team works appears to have had a false alarm. But in another sense, Photos is on fire. In less than two years, Google's service for storing and managing photos has attracted 500 million monthly users. That appears to make it likely one of the fastest-growing consumer services ever.

Photos is Google's fastest-growing product ever — faster than YouTube, Gmail, or Chrome

With a user base in hyper-growth mode and Google's massive resources at its disposal, Google Photos is pressing its advantage. At the Google I/O developer conference today, the team announced useful new features for sharing photos and debuted its first physical goods: printed photo books. It also showed off plans to layer intelligence on top of your photos by turning pictures of business cards into contacts with one tap, for example, or linking your photos of landmarks and paintings to descriptions from Google's Knowledge Graph.

After two years of building, the Photos team says it sees a day when the venerable smartphone camera roll is obsolete — replaced by Photos, an omniscient, ubiquitous guide to the most important images in your life. "You don’t think about your life as a reverse chronological set of photos in order," says James Gallagher, an engineering director on the team. "You think about moments — this is when I started a job, or this is when I got married. That’s what we want our product to be — how we live our lives in photos."

Until recently, it was an open question whether any tech company could bring order to our digital photos. Early services like Everpix and Picturelife sputtered and died. Carousel, a high-profile effort from Dropbox, met the same fate. Flickr enjoyed a brief resurgence before inexplicably starting to charge for features that once were free.

That’s left the task primarily to the giants. Amazon has a ho-hum offering limited to Prime subscribers, and Apple’s iCloud Photo Library is underpowered and expensive. Facebook is the largest photo sharing service in the world, but it does almost nothing to help you organize your private photos.

The more other tech giants flailed, the better Google Photos has come to look

The more other tech giants flailed, the better Google Photos has come to look. Its offer of free, high-resolution storage for all your photos remains the industry’s most generous. Its search and organization features are unparalleled. And its automated tool for turning photos and videos into animated mini-movies makes for excellent reminiscing.

Now the company is turning its attention to one of the most vexing problems in photo sharing: making sure the photos you take actually make it to their intended recipients. There's a graveyard full of startups that have tried to make collaborative smartphone albums easy, and most of them tripped over the same problem: getting people to download a new app and trust it with their photos.

Google has some big advantages in that regard — most notably, Photos is preinstalled on smartphones running the Google version of Android. It also ported over users of its venerable service Picasa, which it shut down last year. And Photos is built to make sharing pictures easy, even if the recipient doesn't have an account, distributing links via email, SMS messages, and the web.

Until now, sharing photos has required you to remember to take action. Within the next few weeks, Google Photos will start suggesting that you share photos you've taken of your friends with the friends it detects in your photos. Facebook has been doing this for nearly two years inside its app Moments. Facebook’s solution is, frankly, more elegant: it knows who your friends are, so matching them with their faces and suggesting you share with them is straightforward.

Google Photos, on the other hand, doesn't know who your friends are, and it doesn't ask. Instead, it makes a series of clever educated guesses. If you send pictures of the same face to the same phone number or email address a few times, Photos will suggest you share your next few photos of that face with that phone number or email address. If your friend is a Photos user, they can save your photos to their own cloud library with a single tap — and if they have photos from the same event, they can share their own photos right back to you. You can also opt in to a feature that makes your own face recognizable to Google in your friends' photos.

I didn't get a chance to test the feature, but I suspect that over time it will work about as well as Facebook's. If Google Photos is already your prime repository for images, that's good news. "It takes all the work out of it," Lieb says. "You still have complete control over what gets shared, and to whom. But it reduces the friction so much. In the best case, it’s literally two button presses."

But the Photos team is also taking it a step further — automating sharing completely between you and one trusted partner. "Some people have a special person in their life for whom it is still kind of annoying to [ask] to hit share," Lieb says. If you have a spouse that you're not cheating on, and kids that you're always taking pictures of, it might make sense to automate that sharing. And so the team built a feature it calls the shared library, which lets one person see your photos as you take them in real time.

Given the sensitive nature of people's photo albums, the devil here is in the details. (The makers of Highlight tried automated library sharing in an app named Roll, and it went over so well that they were out of business four months later.) But the Photos team has been uncommonly thoughtful about how shared libraries work. You can choose to share your entire library if you like, or only share photos of certain people — those kids, for example. You can also choose to share photos only after a certain date — the day you met your partner, for example, so as to spare them the burden of reliving your past relationships.

Once your partner accepts your invitation, they will see whatever photos you've authorized them to see, updated in real time. They can save them to their own libraries if they like with one tap. Over time, the team said, they might let you grant multiple people access to your library — so aunts and uncles and grandmas and grandpas all get access to photos of a new baby, for example. But not anytime soon. "We’re gonna take it slow, and maybe do that," Lieb says. "But we need to nail this use case first. Are the controls we’re providing the right controls?"

Google Photos' third big announcement at I/O is a moneymaker: photo books. Nearly every photo service on the internet offers some form of photo books, and while each company brags about the quality of their own offering, in my experience they are all basically the same. What they have in common is that they make for pretty good gifts, and they offer enormous profit margins to their makers. Google Photos' photo books are no exception.

You can make one on your phone or on the web, starting at $10 for a softcover 7-inch square book and $20 for a 9-inch hardcover book. In both cases, that cost covers only the first 20 pages — which isn't a ton of photos, particularly if you've just taken a big vacation. Each additional page is $0.35 to $0.65, and it adds up in a hurry: a sample book I made about a vacation to Italy wound up costing me $55, which is probably at least $50 more than it cost Google to make.

Google plans to market the books aggressively through prompts in the app. Just return from a trip? Expect to get a notification inviting you to make a photo book. The team told me it hopes to make photo books an item that people buy multiple times throughout the year, as opposed to annually or less. "It’s not just about the book that you make at the end of the year to capture the entire year," says Aravind Krishnaswamy, another engineering director at Photos. "It can become this lightweight thing you do a lot more often."

The new sharing mechanics are genuinely useful, and photo books make for nice tchotchkes. But much wilder stuff is on the horizon. Every major tech company is investing in machine learning, but Google's take on artificial intelligence is connected to the Knowledge Graph — its semantic understanding of thousands of concepts. That means that it can connect images it recognizes in photos and videos to useful information in Google's libraries — and then offer up that information in context.

Google calls its set of image recognition technologies Lens, and to start you’ll find Lens in Photos and the Google Assistant. (In the Assistant, you use Lens as you’re capturing images through the viewfinder; in Photos, Lens adds a layer of intelligence to photos you’ve already captured.) At I/O, the Photos team planned to demonstrate a few of its proposed applications. Say you've taken photos of your favorite paintings at a museum you visited. Google knows what those paintings are, and in time you'll be able to learn about them directly inside Google Photos — just tap the Lens icon and a description will pop right up.

Photos will morph depending on your own preferences

There are more prosaic uses as well. Eventually you'll take a picture of a business card and, if you like, Google will add it directly to your contacts. Or it will bring together all the photos of receipts you've taken into a single place. If your team at work does a lot of work on whiteboards, Photos will bring all your whiteboard photos into a single place, too.

Over time, your own results will become more personalized. Some people want to see all of their receipts at the top of the Photos app; others want them to be hidden by default. Photos will morph depending on your own preferences, says Anil Sabharwal, who runs the Photos team.

In that world, your camera roll will no longer be your default view of the photos you've taken. The standard gallery app will lack so much of the context you have become used to: the names of the people in the photos; information about the photos' contents; a search function that finds objects within them. The gallery isn't organized into events, and it doesn't include your friends' photos. The receipts and whiteboards are mixed in with selfies and photos of your kids. It's a mess — and the messier it gets, the easier it is for Google Photos to win.

Photos users upload 1.2 billion images a day

"My grandparents probably took 60 photos in their lives," says Leslie Ikemoto, who heads up machine learning at Photos. "I took 60 pictures this weekend." Already, Photos users upload 1.2 billion images a day to Google's servers. In the future, she said, we'll wear devices that capture 60 pictures per second.

And if that's the case, it will no longer be enough to store your photos. The companies that we trust with our memories will have to understand those photos, too. "Suggestions, patterns, the people that are important in your life — how we bring those to you at the appropriate time," Sabharwal says. "Everyone is different." It's a huge challenge. But organizing the world's information and making it useful has always been Google's favorite thing. And half a billion people are now helping the company figure it out.