yii, extension to use for image thumbnail generation :
http://www.yiiframework.com/extension/justintimeimageresizer/
And this extension requires this extension :
http://www.yiiframework.com/extension/image/
http://www.yiiframework.com/extension/justintimeimageresizer/
And this extension requires this extension :
http://www.yiiframework.com/extension/image/