You don't realize how important batch processing is until you are faced with 50 photos that need to be resized from 3872 x 2592 to 640 x 480. Processing each photo one-by-one in an image editing app would take an hour. Instead of wasting your time with such a tedious task, you can turn to an app like Image Bucket, which will do all the work for you.
Image Bucket is a batch image processing app for OS X. It'll let you resize, flip, rotate and watermark a group of images all at once. You can even change the file format of an image or modify the name of a file by tacking on a prefix or postfix.
The app can sit in the dock or at the side of your desktop. You simply select the files or folders you want to batch process and drag them onto the app. This will open a dialog box with all the different resize, rename, and watermark options. Select your option, click start and sit back while the images are processed. The app is pretty fast; a batch of 10 images takes about 5 seconds to process.
The batch tool does a good job modifying the images, but it's not perfect. The rename option doesn't fully rename the files. It adds a prefix and a postfix, but won't replace the name. This is inconvenient when you're doing screenshots and want to get rid of the date and time stamp in the image's name. The app also doesn't have any algorithm options for resizing. As a result, the images are not as sharp as they could be. This is fine if the image is going to end up on a general website, not so good if you want it to showcase your photography skills.
Overall, I am pleased with Image Bucket. It's a nice companion to Pixelmator which I use for basic image editing. It's fast and always available in the dock which makes it easy to use. And for $3.99, it's priced favorably, too.