Updated December 2022

1. Simple method in Word document:

1. Select the image, go to Picture format
2. Select Compress
3. Save

2. Resize multiple images in a document

1. Insert the pictures in the Word file
2. Use the Reduce File Size option (under the File menu)
3. Save

You can also do the same for PowerPoint files but the command is “Compress Pictures” rather than “Reduce File Size”. It's also in the File menu.

The MS Word methods are probably enough for 99% of cases but for interest:

1. Resizing a group of images on a Mac

1. Select the images you want (you can use the shift key and sweep the mouse across a group of files, or add them one by one by using cmd-click).
2. Open them in Preview (cmd-O)
3. Under the “Tools” menu, click “Adjust size” and then change it there.

For more details, see this blog post:

https://www.idownloadblog.com/2013/10/19/how-to-resize-multiple-images-mac/

2. Email method:

1. Attach a bunch of photos to an email to yourself
2. Use the option to resize them to save memory
3. Save the email and then use those resized pics.

You can also save the images that you have resized in your Word or PowerPoint video.