png image doesn't show

Hello all, I have been trying to modify the working of one of my pages which prints a png graph. What I had was an included file named "graphit.php" which creates a png file. I used the function imagepng($image,'temp.png') to create an image and then used <img src=temp.png> to have the image printed on the page. This worked well enough when only one user (me) was using the page, but I want more. In reading the imagepng() info in the manual, it states that I can output the raw image stream to the browser by leaving off the file name option. I've done this, but get nada! How should this be done? One of the notes (and it's in German) implies that I can call "graphit.php" using something like <img src=graphit.php> to get the image output. Unfortunately, I get nothing except the red X indicating a missing image. Any and all help is greatly appreciated. Hugh