title: What is a PHP header?
body: <p>I'm wondering about what PHP headers are. I use PHP strictly for HTML completion and I thought I had to send text/html header when the output was text and then image/jpeg header from a separate script which was used as source in an image tag but then someone suggested me to take away the headers because they made nothing.</p>
  
  <p>I did and everything was the same as before. This made me wonder: What are headers? When are they used? (both from an HTML perspective but also from some (?) other perspective) And why could I remove mine?</p>