On a Mac...
1. Get all of your photos into a single folder
2. Right click on the folder (highlighted in pink). If you are using the default Apple trackpad, TAP down with two fingers. If you are using a mouse (any brand), press CONTROL and right click at the same time.
3. Click Compress "FOLDER NAME" on the menu that appears. In this example, I named the folder, "To Zip". Therefore, the menu option is Compress "To Zip"
4. After you press that option, your new zipped folder should show up right below the original folder