You can make the text easier to read by inserting a black jpg before the met text and adjust the dimensions to suit. The first set of numbers is X and Y, the other is the size of the jpg (which is simply just some black pixels) and the last number (80) is the transparency.
$black = imagecreatefromjpeg('black.jpg');
imagecopymerge($image, $black, 270, 678, 0, 0, 765, 30, 80);