PHP, display image with Header()

Question

I'm displaying images from outside my web root, like this:

header('Content-type:image/png'); readfile($fullpath); 

The content-type: image/png is what confuses me.

Someone else helped me out with this code, but I noticed that not all images are PNG. Many are jpg or gif.
And still they are displayed successfully.

does anyone know why?

Answer 1

The best solution would be to read in the file, then decide which kind of image it is and send out the appropriate header

$filename = basename($file); $file_extension = strtolower(substr(strrchr($filename,"."),1));  switch( $file_extension ) {     case "gif": $ctype="image/gif"; break;     case "png": $ctype="image/png"; break;     case "jpeg":     case "jpg": $ctype="image/jpeg"; break;     case "svg": $ctype="image/svg+xml"; break;     default: }  header('Content-type: ' . $ctype); 

(Note: the correct content-type for JPG files is image/jpeg)

Answer 2

There is a better why to determine type of an image. with exif_imagetype

If you use this function, you can tell image's real extension.

_{with this function filename's extension is completely irrelevant, which is good.}

function setHeaderContentType(string $filePath): void {     $numberToContentTypeMap = [         '1' => 'image/gif',         '2' => 'image/jpeg',         '3' => 'image/png',         '6' => 'image/bmp',         '17' => 'image/ico'     ];      $contentType = $numberToContentTypeMap[exif_imagetype($filePath)] ?? null;          if ($contentType === null) {         throw new Exception('Unable to determine content type of file.');     }      header("Content-type: $contentType"); } 

You can add more types from the link.

Hope it helps.