It can be hard to describe the grainy appeal of an Instagram photo. Conceivably it’s a yearning for the nostalgia of yesteryear, a push back against the perfectness of modern photography. Maybe it’s the utilitarianism of the tool, the fact that anyone (using either Apple's iOS or Google's Android) can be a photographer, artist, and curator.

Perhaps it’s simply the fact that you can put a picture of, say, your dinner through the “Lo-fi” or “Earlybird” filter, blur out the edges and tap that sunshine button, and suddenly the everyday becomes exotic.

Whatever the reason, Instagram has, almost overnight, become a shutterbug staple. In fact, analytics firm comScore announced last week that the 2-year-old app reached some 7.3 million daily active mobile users in August, surging past the likes of microblogging monarch Twitter.

For the traveler, Instagram has become somewhat of a postcard-maker for the digital age. We can send through the (cyber)mail a little nugget of our travels. It can reach a wider audience of our friends, family, and colleagues, instilling that tinge of envy that every traveler secretly pines for: I’m here. You’re not.

That’s exactly what a friend and I did on a recent trip to Chile. Though we had not one but three nice cameras (one for my pocket, one for each of our necks), we found ourselves taking as many snapshots with our iPhones. The immediacy of sharing those filter-fixed photos on Instagram and receiving instant feedback became addictive.

The normal routine, after all, is to take the dazzling photos, go home, touch them up, and share them with friends and family about a week or two after your vacation has ended -- once you’re done unpacking, done answering old phone calls and emails, and reached the point where you realize you’re not on vacation anymore and want to relive it.

With Instagram, you can share your travels as they happen -- or at least as soon as you can find a Wi-Fi connection. When the trip is complete, you have your own photo diary of the journey, compiled with minimal effort and artistic (read: grainy, fuzzy, high contrast) flair. And if you’re like me and your iPhone slips out of your pocket during a cab ride on your last day abroad, you have the bittersweet knowledge that your photos are safe and sound, waiting patiently in the ether to join you on your next phone when you re-download the Instagram app.

Photos via NYCOnMyiPhone and Fbascug