Part of writing about the Mac involves taking screenshots - lots and lots of screenshots. Anyone can snap a screenshot by pressing Command-3 to capture the entire screen or Command-4 to specify an area to be captured, but when you're creating hundreds of images, those tools are too blunt. Instead, I use Ambrosia Software's excellent Snapz Pro X, which offers much more control over what can be saved: the entire screen, a window or object (such as a single pop-up menu), or a user-defined rectangle (both for still images and movies). For the most part, I use the object capture feature to grab stuff like the iMovie interface or System Preferences window.
When Apple introduced Mac OS X, however, it threw a kink into this screenshot system: unlike Mac OS 9, windows in the Aqua interface have no borders; they're defined by their content and a drop shadow that makes them appear as if they're floating above other windows. When I would take a screenshot using Snapz Pro X's object-level capture, the drop shadow isn't included, which often led to a problem when a white dialog (such as the System Preferences window) would be printed on a white page: with no definite borders, the image can be confusing. Ambrosia introduced the capability to specify several border types as a result, including a Drop Shadow option, but it's a bit darker than the Aqua version; it also can't be used when I need to build a screenshot that includes more than one window, since applying the Snapz Pro X drop shadow would create the shadow around the entire capture area, not to each element.
One method of capturing native Aqua shadows has been to position a blank Microsoft Word (or other word processor) document behind the objects I want to grab, or set my Finder desktop image to white. But those options are clumsy. Instead, for a recent project I used John Haney's free Backdrop 1.4, a 103K download.
When I need to capture a screen, I bring Backdrop to the front, which obscures my other applications, and then click the program I need to shoot so that it's the frontmost application. Then I invoke Snapz Pro X. It's that simple.
Backdrop works well with multiple monitors, so I'm able to use my PowerBook's screen (my secondary display) for capturing images and my Dell 2005FPW monitor (my primary display) to work in Word, InDesign, or another application. In fact, Backdrop's preferences enable you to specify whether the program works on all displays or just one (it recognizes up to five).
You can also control whether Backdrop sits between applications as if it's just another program (which it is) or if it blanks out the desktop image and leaves icons visible (thereby saving you the trouble of switching in and out of the Desktop & Screen Saver preference pane).
And you're not limited to white. You can set any color as your backdrop. There are also a collection of Pixel Test colors (red, green, blue, black, white) to help you spot-check the quality of your monitor.
Finally, you can choose to display images. How is that different from setting a desktop image? You can create a reference image such as rectangles denoting common Web screen dimensions. For example, as I'm updating my book iMovie HD 6 & iDVD 6 for Mac OS X: Visual QuickStart Guide, I'm using this feature to maintain a consistent iMovie window size.
I'm also tempted to try using Backdrop as an anti-distraction agent, as Merlin Mann recently suggested on his 43 Folders site, which focuses on time-management techniques such as the David Allen's Getting Things Done system.
As I mentioned, Backdrop 1.4 is a free utility, and it's recently been updated as a universal binary to run natively on Intel-powered Macs.