ob_clean這個函數的作用就是用來丟棄輸出緩沖區中的內容，如果你的網站有許多生成的圖片類文件，那麼想要訪問正確，就要經常清除緩沖區。
If you work on an extremely large project with a lot of source and required files, like myself, you will be well-advised to always clear the output buffer prior to creating an image in php.
