The image macro features a picture of Gordon Freeman, usually referencing the game or talking about crowbars(the main weapon of the series, Half Life, of which Gordon is the main character).
Notable Examples
<img src= "http://chzmemebase.files.wordpress.com/2011/04/memes-you-are-now-reading-this-in-my-voice-oh-wait.jpg"> <img src= "http://chzmemebase.files.wordpress.com/2011/04/memes-id-hit-that-with-a-crowbar.jpg"> it originated in the community forums on steam and the game itself(needs citation)