Resize Image In Mac App. The built in preview app can be a good place to start if you want to optimize your images. Enter the width or height value to resize your photos to your liking.
Right click and choose open with preview. In the folder with your images select the ones you need to resize and then right click on them and choose open with. Resize a single photo on mac with preview app this app is often a default photo viewer on mac computers so in order to open your photo in preview app you just need to find the folder in which it is stored and double click on it.
Click the edit button a square with a pencil to switch to.
This will open the image in preview. Right click and choose open with preview. Now go to tools. Although probably not your best option preview does allow for batch resizing.