Transferring photos from other people's phones to my iMac.

1 - Connect the iPhone to your Mac via USB cable and launch Image Capture.

2 - unlock the iPhone.

3 - when asked on the iPhone trust the computer.

4 - you'll be asked to unlock the iPhone again on the iPhone.

5 - select the photos you want to download and select the location.

6 - click on Import button.

When Mac and iPhone are signed in with different Apple ID and password on the same network see these articles https://support.apple.com/en-in/guide/iphone/iph3d2676c9/ios

https://support.apple.com/en-in/guide/icloud/mmc0cd7e99/icloud

If Mac and iPhone are signed in with same Apple ID and password on the same network see the article https://support.apple.com/en-in/HT201302