image problem

hi all im trying this simple code for images and seems doesnt work it outputs characters instead of an image plz let me know how do i output image and do i need to use header if yes how $im = imagecreatefromgif("images/city.gif"); // setpixel is in loop imagesetpixel($im,$i,$i,99); // loop ends imagegif($im); Output is code like this in place of image ñ  $J”(Q¢@8è †D‰
thÜ!?$XÐàA„$L˜0a„ &L˜P ƒ„ &L˜Pà¡q‡&L˜p ƒ„ &L˜0a„ &L˜0a„?;?À? <ˆ0¡Â… :|1¢Ä‰?;AD‘"EŠ)R¤H1â¡q8?`Aƒ&T¸?aC‡ Thanx in advance -- Warm Regards Deepesh