PHP exif_imagetype note #1
Windows users: If you get the fatal error "Fatal error:  Call to undefined function exif_imagetype()", and you have enabled php_exif.dll, make sure you enable php_mbstring.dll. You must put mbstring before exif in the php.ini, i.e.:extension=php_mbstring.dll
extension=php_exif.dll

You can check whether this has worked by calling phpinfo() and searching for exif.
PHP exif_imagetype note #2
If the function exif_imagetype() is not available,
you can try the following workaround:if ( ! function_exists( 'exif_imagetype' ) ) {function exif_imagetype ( $filename ) {if ( ( list($width, $height, $type, $attr) = getimagesize( $filename ) ) !== false ) {return $type;}return false;}
}
PHP exif_imagetype note #3
By trial and error, it seems that a file has to be 12 bytes or larger in order to avoid a "Read error!".  Here's a work-around to avoid an error being thrown:// exif_imagetype throws "Read error!" if file is too small
if (filesize($uploadfile) > 11)$mimetype = exif_imagetype($uploadfile);
else$mimetype = false;
PHP exif_imagetype note #4
Seems to give a 'Read error' warning if the size of the file is very small (2 bytes). I think this is because it needs a min 3 bytes to determine the file type
PHP exif_imagetype note #5
libexif can also be used to parse image info out of id3 tags:exif_read_data("mp3_with_2.4ID3TAGS, '', true, false);
PHP exif_imagetype note #6
After looking for hours, I found a very good source for exif related programs here: http://drewnoakes.com/code/exif/index.html
It lists exif specifications (pdf), a few good links to exif related stuff. The best source I have found in my quest to understand exif better for use in php based exif tools.

  if ( ! function_exists( 'exif_imagetype' ) ) {

          // $currFile = $file['tmp_name'];          list($width, $height, $type2, $attr) = getimagesize($file['tmp_name']);           $type = $type2;          // function exif_imagetype ($currFile) {          //   if ( ( list($width, $height, $type2, $attr) = getimagesize($currFile) ) !== false ) {          //       // return $type;          //     $type = $type2;          //   }          //   return false;          // }        }else{           // $type = exif_imagetype($src);          $type = exif_imagetype($file['tmp_name']);        }