The image carried the words, "over 1,057,000 people have been killed by guns in the USA since John Lennon was shot and killed on 8 Dec 1980."
Posting the tweet, 44 years to the day after the couple wed, she said: "The death of a loved one is a hollowing experience."
The death of a loved one is a hollowing experience. After 33 years our son Sean and I still miss him. Yoko Ono Lennon http://t.co/PYigb2uJKT
John Lennon was murdered on December 8, 1980, outside his New York apartment.
He was shot four times in the back by Mark Chapman who had asked for his autograph only hours before.
Together, let's bring back America, the green land of peace. http://t.co/Al3PWTC4aZ
31,537 people are killed by guns in the USA every year. We are turning this beautiful country into war zone. http://t.co/vT2gLjwUZV