Suppose you have a folder full of photos taken in rapid succession. These might be images from an MRI or ultrasound, or simply a sequence of shots snapped at a celebration of some sort. Either way, you’ve ended up with a series of photos that would likely look good animated—but they’re all simply stills.

There’s an easy way to put those photos in motion. Single-click on the first one in your folder, and then press the Spacebar to bring up the Quick Look preview of your image. Now, simply hold the down arrow. The Finder selection will cycle through all the photos in your folder, and the Quick Look preview will instantly update in real time.

If your folder contains photos that work as a flip book, you can see the animation right there in the Finder using this method.

Source: Mac OSX Hints