Occasionally, when you are working with a template or a frame, your photo is just short of covering the placeholder.
You can always increase the size of the photo, but keeping it in proportion may mean you have to hide a portion of the photo you want to keep for content or balance.
Sometimes "cloning in" a section with the clone stamp tool works, but on some images, cloning is obvious.
Fortunately, the latest versions of Photoshop CS (the full-version) have an almost magical feature called "Content-Aware Scale" that is designed for just this situation. Here's how to use it:
Open a new document and an image in Photoshop.
Get the Move tool and drag the photo onto the new document.
Select the photo layer by clicking on it.
Get the Rectangular Marquee tool and drag out a selection that completely encompasses one edge of the photo.
Press the letter V on the keyboard to get the Move tool.
Choose Edit > Content-Aware Scale from the Menu bar.
Get one of the square handles on the side of the bounding box and drag out to the boundary of your new size.
Click the checkmark in the Options bar to confirm the change, the press Ctrl D (Mac: Cmd D) to remove the selection.
Photoshop's Content-Aware scale will fill in the details of the photo, so that it doesn’t look obvious that you've added a section.