Most mobile photo-editing apps are the kind you'll use occasionally, like when you need to crop an image before uploading to Flickr.  Instagram, however, gives you a reason to keep coming back - it doubles as a social networking hub.

Want to jazz up your pictures?  With over a dozen Lomo-like filters on tap, it lets you fashion your image captures in a slew of creative ways, making regular smartphone photos look like fancy, artsy shots.

Instagram's strength, however, lies in its "life-sharing" feature.  Think of it as a Twitter-like service, except all your updates are made up of photographs.   They have their own social service where you can add contacts, post photo updates and browse through your friends' photo streams.   Even better, they've tightly integrated other popular social networks, allowing you to share your pictures on Twitter, Flickr, Facebook, Tumblr and Foursquare.  For the last one, it will even geotag your image, so that Foursquare can use it to add a place-name.

You will need to sign up for an account right from the app, of course.  Once you get that done, though, you can immediately begin using all the features.  Layout is very intuitive, so you should have no problem figuring out what to do.

Overall, Instagram is just the kind of service you expect to hit it big - fun, socially-connected and feature-packed.  There aren’t likely a lot of folks in your contact list using it now, but expect that to change over the next few months.  You can download it free from the App Store.

[Instagram]

I love HDR photography.  When you get it right, the photos look gorgeous, with amazing detail.  When it's wrong, the shots are beautifully freaky, like a still from a vivid dream.  To me, it's a winner both ways.  You would think I'd love the HDR Camera for iPhone app.  Well, I don't.

Typical HDR systems take several shots of the same scene with staggered exposures.  Combining these different images into one, you end up (well, sometimes) with a single shot that fits in more detail than a regular photo taken with the same lens.   That's not what the HDR Camera app does.

Instead, it adds a selection of filters that mimic HDR effects on your iPhone, which you can then apply to single-shot photos you take on the device.  In function, it's actually more like a photo-editing software than a camera tool - something you can probably get with better options on a desktop application.

HDR Camera offers eight different filters.  Once you select an image, you can then try the filters one by one, saving the particular combination that you're happy with.  There are no adjustment settings, so cycling through all eight options is all the tweaking you get to do.  Depending on the image and the effect, results can vary from decent to strange.  Mostly strange, though.

Personally, I love the resulting images from the filters.  None of them resemble anything I will dare call life-like, however.  In fact, I find the output to be a little on the extreme (which I appreciate), something I don't think majority of people looking for an HDR app is actually going for.

Available for $1.99, HDR Camera is a fairly-decent app.  There's nothing in it that you can't get someplace else, though (probably for free).  In fact, you can skip it and probably not miss a thing.

[Macphun]

Even though iPhone comes with some amount of photo filtering, it is decidedly inadequate, especially for those of us who enjoy dressing our images in interesting manners. For the most part, I don't find it that much of an issue since I can fashion photos in a myriad of ways once I put them on my PC. However, I sure would appreciate being able to do fancy modifications right on the phone as well.

The 99-cent app 101 PhotoFilters fits the requirement nicely, offering 102 (yes, missed the mark by one) different alterations to images stored on your phone. It comes with a nice set of options that include traditional filters (like grayscale and overburn), creative new modifications and some inanities. Quite a few of the filters do border on the frivolous, though I count at least 30 or so that I'll probably be using regularly.

Using the app is not the most intuitive process, though it's usable enough once you get the hang of the controls. The opening sequence is particularly dumbfounding, basically going against your natural navigation instincts.

Filtering is pretty fast, with a progress bar showing you the status of the update. Changes are not automatically committed so you can easily try a different filter or revert to the original photo in case you choose one that's not to your liking. You can also layer multiple filters on a single photo, which can lead to pretty impressive results.

With 102 filter options, 101 PhotoFilters is a pretty good use of your app dollar. It's a very worthwhile tool that I wouldn't mind keeping on my iPhone for the long haul.