How to add recipients photos in Mac Mail sent folder?

O/T Hey Old Toad... a lifetime ago you showed me how you had recipients' photos in your Mac Mail Sent folder.

All I've ever been able to achieve is my own ugly mug, which is of no use to me at all!

ChatGPT says it can't be done, yet you did it. Can you remind me how? Thanks!

And I send my apologies to hans184!!!