This application will let you create thumbnail images for any photos or images. After the thumbnails are created, they are opened with Preview.
First, you will be asked to select images. Next, you can set the size and extension for the thumbnails. After that, the images will be opened with the Preview application.
Automator Workflow
Step 1: Ask for Finder Items
Step 2: Create Thumbnail Images
Step 3: Open Images in Preview (no options)