The image extension (http://www.yiiframework.com/extension/image) is very easy to use.
It works stable, but from an old version of Kohana.
Today I want to add water mark into an image, and I do not find any extension.
And I happened to find that new version of Kohana has already supported wartermark.
Then I upgraded the extension, and be here to share it:)
And you should find the document here http://www.yiiframework.com/extension/image, I just upgrade it.
Notice:There is no driver for ImageMagick, it was alternated by Imagick. You should install Imagick php extension.