How to Easily Batch Resize Images on Mac

Do you want to resize multiple images, simultaneously, on Mac without using any third-party software? Batch resizing of images can be easily and quickly done in OS X using the included Preview application.

For batch image resize on OS X Mountain Lion:

  1. Open Finder and select all the image files that need to be resized.
  2. Drag and drop all these selected files on the Preview icon in Dock.  Alternatively, you can right-click and select Open With -> 
  3. Preview will open displaying the selected images as thumbnails in left sidebar.

Resizing Multiple Pictures At Once Preview

  1. Select all thumbnails by either pressing [command + A] or  by selecting Edit -> Select All from the menu.
  2. Select Tools -> Adjust Size from the menu.  Choose your desired image size and you are done!  The resized images are auto-saved and, by default, the image files are overwritten.

Tip: The selected images can also be converted to a different format, from within Preview, by selecting File -> Export Selected Images from the menu.