(PHP 4 >= 4.0.2, PHP 5, PHP 7)
imagetypes — Return the image types supported by this PHP build
Returns the image types supported by the current PHP installation.
   Returns a bit-field corresponding to the image formats supported by the
   version of GD linked into PHP.  The following bits are returned, 
   IMG_GIF | IMG_JPG |
   IMG_PNG | IMG_WBMP | 
   IMG_XPM.
  
Example #1 Checking for PNG support
<?php
if (imagetypes() & IMG_PNG) {
    echo "PNG Support is enabled";
}
?>