One of the best lectures I ever attended was by Karsh - and he had slides!
I was working as a photographer for a newspaper at the time, so I photographed him giving the lecture. His response - a large wink
Sadly, the light levels were such as to permit slide shows - the "wink" photo was too blurred to be usable.
That was where I saw the alternate version of Winston Churchill's portrait - with Churchill smiling.
Interestingly enough, Yousuf Karsh's brother, Malak Karsh was also a fine photographer in his own right. It was his photograph that graced the back of Canada's $1.00 bill, when we had a $1.00 bill. In what may be an archetypical response of a successful immigrant to Canada, he was known throughout most of his professional career by his first name, Malak, because it made it less likely that he and his brother would be confused.
There is a lot to be learned from either of them.