PopAGraph is a free iOS app that lets you mask off something in a photo, then create a reduced size frame that lets the object pop put of the frame boundaries. It can give your photos a unique look, and it's something I haven't seen before in an iPhone app.
To make it work you select something in your image that you want to stand out. You draw a mask with your finger. You don't have to be exact, because the app will try and find the edges of the subject if it is pretty well set off in contrast of color. You can enlarge the view for more precise masking, and pan around using 2 fingers.
When you are satisfied, you touch the 'lift' icon, and your selected object will be separated from the background. Select a frame, or multiple frames. They must be smaller than your masked object so the object can extend beyond the frame. You get a choice of frame colors and styles. The end result can be quite striking. You can then send your fished product via email, instagram or Twitter. Of course you can also save to your local photo library.
PopAGraph is a clever photo editor. You're not going to be able to jump right in, because not every step is intuitive. There is, thankfully, built in help with video tutorials that make the operation of the app clear enough. The app also has some nice filters, so after the masking process you can change the background or the foreground. For example, leave what has been masked in color, and turn the rest of the photo black and white. There are more extensive filters, but they involve an in-app purchase. If you buy everything, including more frame options, the app is U.S. $2.99 instead of free. I found I could get along with what is included in the free version.