I was looking for a way to add kerning to my text and finally just made this function to do it. Of course, if you're generating the size of the image based on the text you're putting in it, you'll have to figure out the new size to fit the new text width but I'm sure you can figure that out.
for($i=0;$i<strlen($text);$i++){
// Get single character
$value=substr($text,$i,1);
if($pval){ // check for existing previous character
list($lx,$ly,$rx,$ry) = imagettfbbox($fontsize,0,$font,$pval);
$nxpos+=$rx+3;
}else{
$nxpos=0;
}
// Add the letter to the image
imagettftext($im, $fontsize, 0, $nxpos, $ypos, $fontcolor, $font, $value);
$pval=$value; // save current character for next loop
}
