In this post explains how to create thumbnail image using php code.

function make_thumb($img_name,$filename,$new_w,$new_h)
{
//get image extension.
$ext=getExtension($img_name);
//creates the new image using the appropriate function from gd library
if(!strcmp(“jpg”,$ext) || !strcmp(“JPG”,$ext) || !strcmp(“jpeg”,$ext) || !strcmp(“JPEG”,$ext))
$src_img=imagecreatefromjpeg($img_name);

if(!strcmp(“gif”,$ext) || !strcmp(“GIF”,$ext))
$src_img=imagecreatefromgif($img_name);

if(!strcmp(“png”,$ext) || !strcmp(“PNG”,$ext))
$src_img=imagecreatefrompng($img_name);

//gets the dimmensions of the image
$old_x=imagesx($src_img);
$old_y=imagesy($src_img);

$ratio1=$old_x/$new_w;
$ratio2=$old_y/$new_h;

if($ratio1>$ratio2) {
$thumb_w=$new_w;
$thumb_h=$old_y/$ratio1;
}
else {
$thumb_h=$new_h;
$thumb_w=$old_x/$ratio2;
}
// we create a new image with the new dimmensions
$dst_img=ImageCreateTrueColor($thumb_w,$thumb_h);

// resize the big image to the new created one
imagecopyresampled($dst_img,$src_img,0,0,0,0,$thumb_w,$thumb_h,$old_x,$old_y);

// output the created image to the file. Now we will have the thumbnail into the file named by $filename
if(!strcmp(“png”,$ext))
imagepng($dst_img,$filename);
if(!strcmp(“gif”,$ext))
imagegif($dst_img,$filename);
else
imagejpeg($dst_img,$filename);

//destroys source and destination images.
imagedestroy($dst_img);
imagedestroy($src_img);
}

?>

To find out the extension of image with following function:

function getExtension($str) {
$i = strrpos($str,”.”);
if (!$i) { return “”; }
$l = strlen($str) – $i;
$ext = substr($str,$i+1,$l);
return $ext;
}

Call the particular thumbnail function like :

make_thumb(‘original.jpg’,'thumb.jpg’,150,250);
echo “Thumbnail created successfully…!!!”;