dynamic PNG image generation

hi I am using PHP4.0.4 to dynamically generate a PNG image with code like <? 126 header ("Content-type: image/png"); 127 $im = ImageCreate(50,100); .. .. .. 201 ImagePNG($im); ?> This code is embed in HTML file. The number on right are lines numbers just for reference. I got error "Cannot add header information -- header already sent by /var/www/html/php4/physics_01.php4 on line 126." appears apache server is parsing the output and return this error message in response to find "header information generated by line 126. I have 2 questions 1. Is there a way to test script outside apache -- without a web server running. 2. Is this an apache configuration problem? I am using the default configuration which works fine for mime type text/html. Thanks for your help. rjae-1@att.net