We’ll start with a straightforward action, one which will take images from the Finder and resize them when you drop them onto the application icon on the desktop.
Launch Automator, either from the Applications menu, by typing its name in Spotlight, or by using the search bar in Launchpad.
When the template chooser is displayed, select Application then click Choose.
In the Library, click Files and Folders and drag Copy Finder Items into the main window.
Click on the dropdown menu next to ‘To’, select Other and create a new Folder in Pictures called ‘Resized.’
Add a Rename Finder Items action to the workflow, choose Add Text from the dropdown and type ‘–resized’ into the box.
Click on Photos in the Library, and drag Scale Images into the workflow.
Choose Don’t Add from the warning dialog, since we already have an action to copy the files in the workflow.
Type the width of the resized image into the box if you want to resize to a specific width, or choose Percentage from the dropdown menu and type in the size of the new image relative to the old one.
Save the workflow to the desktop as an application with a descriptive name.
Now, whenever you drop an image onto the application, it will be copied, resized and the copy placed in the Resized folder.