I'm always on the lookout for apps that take advantage of the iPhone's technology for useful or fun effect. One such app is Photoloupe, which uses the iPhone's gyroscope to let you pan across high-resolution photos.
With the pixel count continually increasing on each generation of iPhone, if you have a late-model iPhone, you likely have high-resolution images that contain details not seen on the iPhone's 3.5-inch screen. Photoloupe lets you take or import photos and then take a closer look by zooming in and tilting the iPhone to pan across the image.
If Photoloupe sounds appealing, it would be best to act fast; the app is currently free but only for a "very limited time."
To get started, tap the camera lens icon in the lower-left corner to take a photo or import one from your camera roll (but not Photo Stream), Dropbox, or from iTunes when your iPhone is connected via USB to your PC or Mac. Your photos are then added to Photoloupe's Photo Wall, which includes a number of sample shots. (To delete a photo, tap the Menu button in the upper-left corner when viewing a photo and then tap the delete button in the lower-right corner.)
From the Photo Wall, tap a thumbnail to view the image. You can zoom in and out using the controls in the lower-left corner. To pan across the photo, simply tilt your iPhone. It takes a little getting used to before you'll feel like you have good control, and you can adjust the sensitivity of the gyroscope (or turn it off completely) using the slider in the lower-right corner. To stop panning without attempting to keep your iPhone perfectly flat, just tap and hold on the photo (the pin icon in the upper-right corner will move and glow to show that you have stopped the image). To go to the next photo or return to the Photo Wall, tap the button in the bottom center of the screen.
I don't know how much of a need I have for Photoloupe, but it is a fun and free (for now) app and a great way to show off iPhone technology. I think it would be more useful on the larger screen on the iPad, but, sadly, Photoloupe is built only for the iPhone and iPod Touch.