The 4c stamp was issued in Dec.,1980 illustrating radio waves connecting Echo I and Earth. Echo I is world's 1st communications satellite, placed in orbit by NASA on Aug.12,1960.
The 6c stamp is from Natural History issue in 1970 to celebrate the centenary of American Muesem of Natural History in NYC.
The 44c stamp at the left is from The Simpsons issue in 2009.
The Simpsons, currently in its 20th year as a regularly scheduled half-hour series, is the longest-running comedy in television history. The show is a cultural phenomenon, recognizable throughout the world.
The 44c stamp at the right is Year of the Tiger issue in 2010.