(PHP 4 >= 4.3.2, PHP 5, PHP 7)
imageistruecolor — Finds whether an image is a truecolor image
$image
   )
   imageistruecolor() finds whether the image
   image is a truecolor image.
  
imageAn image resource, returned by one of the image creation functions, such as imagecreatetruecolor().
   Returns TRUE if the image is truecolor, FALSE
   otherwise.
  
Example #1 Simple detection of true color image instances using imageistruecolor()
<?php
// $im is an image instance
// Check if image is a true color image or not
if(!imageistruecolor($im))
{
    // Create a new true color image instance
    $tc = imagecreatetruecolor(imagesx($im), imagesy($im));
    // Copy over the pixels
    imagecopy($tc, $im, 0, 0, 0, 0, imagesx($im), imagesy($im));
    imagedestroy($im);
    $im = $tc;
    $tc = NULL;
    // OR use imagepalettetotruecolor()
}
// Continue working with image instance
?>
Note: This function requires GD 2.0.1 or later (2.0.28 or later is recommended).