If you normally use only one desktop image, but occasionally want to change it to something else, here’s a way to do so that can save a bit of time. Normally, you’d switch the desktop image by opening System Preferences, clicking on the Desktop & Screen Saver panel, clicking the plus sign, navigating to the picture you’d like to us, then clicking Choose. (If you prefer regularly rotating desktop images, of course, it’s much simpler to use a folder of pictures and the Change Picture checkbox in the Desktop & Screen Saver panel.) That’s a fair bit of work just to load one image to use for your desktop.
So here’s a simple, but not necessarily obvious, workaround. Instead of using the System Preferences panel, use either Safari or Firefox 3. That’s right, your web browser can help you easily set your desktop image. In the Finder, navigate to the image you’d like to use for your desktop, then drag and drop it onto the Safari or Firefox icon in the dock. When the image opens, Control-click on it, and choose Use Image as Desktop Picture (Safari) or Set as Desktop Background (Firefox) from the contextual menu. In Safari, the image will instantly appear as your desktop image; in Firefox, you’ll see a small preview window first, click the Set Desktop Background button in the preview window to complete the process.
If you just change your desktop image occasionally, using your browser is a much faster way to do it—not only are there fewer steps involved, but you’ve probably always got your browser running, so you don’t even have to wait for it to launch. This hint should work in any browser that includes the ability to set a desktop image from a displayed image, though I only tested it with Safari and Firefox 3.