On February 5, 1974, the US Mariner 10 probe flew past Venus.

Mariner 10 stamp issued by US post office on April 4, 1975

NASA launched Mariner November 3, 1973, at 05:45:00 UTC. It took 4 months to reach Venus on its way to Mercury. The Mariner managed to fly within 3,584 miles (5,768 kilometers) of Venus. 

Over 45 stamps, from around the world have been issued to commemorate this event.    

Mariner 10 was the seventh successful launch in the Mariner series and the first spacecraft to visit Mercury. It was also the first spacecraft to use the gravitational pull of one planet (Venus) to reach another (Mercury), and the first spacecraft mission to visit two planets. The spacecraft flew by Mercury three times in a retrograde heliocentric orbit and returned images and data on the planet. Mariner 10 returned the first-ever close-up images of Venus and Mercury. The primary scientific objectives of the mission were to measure Mercury’s environment, atmosphere, surface, and body characteristics and to make similar investigations of Venus. Secondary objectives were to perform experiments in the interplanetary medium and to obtain experience with a dual-planet gravity-assist mission. 
NASA – NSSDCA – Spacecraft – Details

In total, 4,165 photos were sent back to NASA by Mariner.