Batch image resize MacOS - Using Preview (yes, its another feature that has been built in to OS X Lion and Mountain Lion)

You can easily batch resize groups of images within Mac OS X by using the included Preview app, there is no need for any additional downloads or expensive photo editing applications, only Preview, which is free with your Mac! Here’s how to do it:

Batch resize images in Mac OS X

1. Select all the images you want resized and open them within Preview (select using the shift key and clicking, and then right-click and choose open with, and then choose Preview)
2. From Preview, select the images that you want to batch resize from the side column showing all the images (Command+A will select them all)
3. Now, go to the menu labeled Tools, and then Adjust Size
4. Enter a value for what you want the new width and height to be
5. Images are automatically saved over the top of the originals as the new size
6. All the images you selected are now resized!

This works in Preview that is included in virtually all versions of Mac OS X!Depending on the power of your machine you can convert thousands of images in one go - my personal record is 14,304 book covers on an i7 MacBook Pro Retina with 16Gb RAM and an SSD, converted into thumbnail form, and it only took around 8 minutes to complete!