I think you people know the importance of gd library in Php. A lot of image functions are there with this. You can reduce the size of an image, resize (physical) , you can convert image format, merge different images, can make the image with round edge, can add watermark, etc etc lot of functions are there. Try to use that .
I will help you , programmer in this. Your referrence link must be: http://au.php.net/gd