I am using this code to creating images with text written in it with transparent backgrounds.
<?php
// Set the content-type
header('Content-Type: image/gif');
// Create the image
$im = imagecreatetruecolor(400, 150);
// Create some colors
$black = imagecolorallocate($im, 0, 0, 0);
$acolor = imagecolorallocate($im, 153, 204, 153);
imagecolortransparent($im, $black);
// The text to draw
$text = 'Testing...';
// Replace path by your own font path
$font = 'arial.ttf';
// Add the text
imagettftext($im, 50, 0, 10, 100, $acolor, $font, $text);
// Using imagegif()
imagegif($im,"img.gif");
imagedestroy($im);
?>
But text which is written in img.gif has some unwanted color(Black) on borders of alphabets(‘e,s,n,g’). How can i finish that color.The generated image is

The arial font download site is http://code.google.com/p/ireader/downloads/detail?name=arial.ttf
The GIF format cannot handle alpha transparency. It can have only 100% transparent (= invisible), or 100% opaque (= visible) pixels.
Your text seems to have anti-aliased, soft edges.
Those edges aren’t 100% transparent, but they’re also not 100% opaque – they are a mixture of foreground and background. That makes them appear softer.
Because the GIF format can’t deal with these nuances, the library uses a mixture of green and black to simulate a “weaker” green.
If you use the PNG format, the problem should go away: PNG supports alpha transparency. There are some issues that you need to look into if you still need to support IE6, but for every other browser, this will work fine straight away.