Some innovations are born as ideas but have to wait for technology to catch up. Witness the tablet computer - a struggling concept long before it was Apple's megasuccessful iPad.

Others are seize-the-moment phenomena - creations that rely on a confluence of events, such as technological advances coinciding with market shifts. Witness Curalate, the latest star to emerge from Philadelphia's burgeoning start-up scene.

At noon Thursday, Mayor Nutter will visit Curalate's Walnut Street headquarters for a ceremonial ribbon-cutting to celebrate its swift growth into a business with 21 employees and 300 client companies, in what an aide calls "our ongoing effort to make Philadelphia a home to start-ups and entrepreneurs."

But the story of Curalate - built on a new search tool for images - is fascinating in itself, both for what it says about creativity and determination and as a window onto the rise of what's known as "the visual Web."

"Consumers are choosing to speak in a new language," CEO Apu Gupta told me this week. "This is about a fundamental shift in consumer behavior that we realized very early on was happening."

How did they come to seize the moment - the moment when Pinterest, where consumers, hobbyists and others post pictures that grab them, was suddenly the new new thing, and when Instagram, Tumblr, and Facebook were exploding with hundreds of millions of new photos each day?

Actually, their success was born in failure - an effort to ride a different Internet wave centered on leveraging "underutilized assets," as Airbnb does by enabling homeowners to turn empty guest rooms into cash.

With cofounders Nick Shiftan, now Curalate's chief technology officer, and Brendan Lowry, its marketing manager, Gupta set out to match people who needed parking or storage space with others who had extra room for cars or stuff.

The three quickly recognized they faced mismatches on both counts. People with scarce parking spaces either needed them or knew their real value - there was little underutilization, in finance-speak. Commercial storage was cheap and abundant, available 24/7 and away from strangers' prying eyes.

The cofounders' first act of genius was in quickly conceding defeat, before they'd even blown through a third of the $750,000 in seed funding they'd gotten from Philadelphia's First Round Capital and two other venture firms.

Their second act of genius, it seems now, was in choosing the idea that became Curalate after their investors told them to keep the money and try again, more interested in the entrepreneurs than in a particular enterprise.

The idea fit their interests and talents. Shiftan, a Harvard-trained computer scientist, was looking for a "big data" problem to solve. Gupta, a Wharton grad who had built the second-largest drugstore chain in India before his mid-30s, was a marketing whiz. And Lowry, barely old enough to buy beer, had grown up a social-media native.

Even more crucial was their timing. Curalate addresses a problem companies didn't know existed beforehand: How to capitalize on the fact that people post pictures of the companies' products on sites like Pinterest. Curalate provides a set of analytic tools to guide them.

Gupta says that when people post, for example, a clothing item they covet, they say, " 'I love this sweater. I've got to have it.' They're not saying, 'This is a Gap sweater.' "

Shiftan's answer centers on a sophisticated algorithm that works much as Shazam does for identifying a snippet of a commercial recording. In less than two years, Curalate has cataloged billions of companies' images, each identifiable by a digital fingerprint - a "perceptual hash," in Curalate's terms.

From there, the marketing possibilities almost seem endless. "Once you know what grabs their eyes, once you know what resonates, then you can use it," Gupta says.

Competitors may challenge Curalate's first-mover advantages. But this much is already clear: Curalate's seize-the-moment idea is resonating, too.