A few things are driving the phenomenon:
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And then there are the already almost countless ways you can manipulate photos right on your phone. I've listed my favorite apps below, as well as apps to help you share photos from the road most easily. Some are faddish, and others are pretty sophisticated. Given that you can run an Express version of world-renowned Photoshop right on your phone, it can't be said that smartphone photo apps are primitive. (And Express Photoshop isn't even the best editing app out there; that honor probably goes to Snapseed, detailed below.)
Two caveats before we start: First, I've focused on the iPhone, partly because I own and use one, and partly because -- at 8 megapixels and with heaps of app support -- the new iPhone camera is way out in front of other smartphone cameras at present.
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Second, I will limit myself to the effect filters that come with the app, or, at least, are free. The number of filters for the more popular apps is astounding, and if you see what you like with any of the apps below, you will soon find lots of ways to expand your horizons from there.
1. The Phone Camera
Let's address the simplest and easiest entry first. The camera on many smartphones -- and the latest iPhone in particular -- is pretty good. On his list of favorite phone apps, electronics expert Grant Imahara simply cited the "iPhone camera." As Imahara says, it is "simple and to the point. Take a picture and then e-mail it to Twitpic. Bam! It ends up on my feed. There are no other lenses or fancy exposure settings. It just takes pictures and that works fine for me."
Many smartphone cameras offer high dynamic range (HDR) capabilities, cropping and flash -- the standard camera features, plus a little more.
Overview: Immensely popular (at present) camera/photo tweaking/photo sharing app.
Instagram enjoyed a vertiginous ascendance in popularity after launching a little more than a year ago (they have 11 million users already), and outside of the generic smartphone upload (to e-mail, text message, Facebook, etc.), Instagram may be the most popular phone/phone sharing app out there. This is primarily for one very good reason: Instagram is exceptionally easy to use, but above all, Instagram is a social photo sharing app. It takes ok photos with lots of available effects (some free, many for purchase), but with this app it's almost absurdly easy to share photos in numerous different ways, typically without ever leaving the Instagram app.
With a native camera app (most of the apps reviewed here have a camera "inside" the app), Instagram sits right in the pocket between very fun and very easy (think Angry Birds), and a traveler could very easily use the app to do an ongoing travelogue from the road.
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There are two things I like about using this app as a camera. First, you can choose the "Normal" filter and Instagram lets you take a typical phone photo. Additionally, you can see how each filter effect will, er, affect your photo before you hit the shutter button. You can apply the filter after the fact as well, but the TTL (through the lens) view is really handy. Then, when you alter a photo with a filter, the app adds the new version to your camera roll, so you have both the original and the new pic.
An important thing to know about Instagram is that there are now apps on top of apps that interface with the main Instagram program, and especially with the sharing capabilities of Instagram. There is also a full cottage industry of folks who will make coffee cups, calendars, gift books and more from your Instagram photo collection. There are photo booth apps, sticker apps and even an app that helps you meet other Instagram users in real life (this could be a very good way to meet folks in distant towns while traveling).
Overview: Camera and photo-tweaking app with a retro hipster Instamatic feel.
When you first open Hipstamatic, it defaults to the "Classic" view through an old instamatic camera, with the old rangefinders that only show a portion of the area the camera actually captured. As if a limited view weren't bad enough, the Hipstamatic default viewfinder is set to be "wandering," showing a random part of the actual image, oof. To change this to "Precision Framing," you have to go into the phone's settings, find the app and change the viewfinder. Whew, that's better.
For the young and hip, Hipstamatic is cool and can be pretty funny. For the traveler trying to record his or her trip, it could work for the occasional Grand Canyon rim flashback family photo, but it's not extremely practical otherwise.