PHP显示为图像

I am trying to make a PHP page load an image and display, as if it were an image file. Here's what I tried to do:

header("Content-type: image/png"); 
echo base64_encode(file_get_contents($ad->location));

But this doesn't seems to work. How should this be done?

Thank you.

You don't need to base64 encode image data when outputting it as a file. Just pass it through.