title: Use PHP to convert JPEGs to transparent PNG
body: <p>I have a lot of JPEG images that I want to convert to PNG images using PHP.
  The JPEGs are going to be uploaded by clients so I can't trust them to make sure they are in the right format.</p>
  
  <p>I also want to make their white backgrounds transparent.</p>
  
  <p>Does PHP have any functions I can use to achieve this?</p>