To resize a bunch of images at once, you don’t have to install Adobe Photoshop or any huge app like that. You can complete the task with inbuilt Terminal app.
To do that, open the Terminal and cd into the folder where the images are in. If you are new to Terminal and don’t know how to navigate using “cd”, then right-click the folder icon and select “New Terminal at Folder”. Click here to see an example.
Make sure you are in the right folder and use the code below.
sips -Z 640 *.jpg
The “640” represents the maximum width and/or height. So, change that accordingly.
The “jpg” represents the extension of the images. Change it accordingly. It can be a jpeg, png, gif and so on.