PHP：imagePNG（）不会将文件保存到目录。文件权限全部正确，仍然无法正常工作

I am writing a program that watermarks user uploaded photos. After completing the layering, imagePNG() outputs the photo to the browser but wont save it to a directory. The paths are all correct and file permissions altered to 0755. Using only the first parameter of the function ( imagePNG($image) ) the image outputs, however when the path is added ( imagePNG($image, "photo_uploads/" . $album_name . "/") ). I am writing a program that watermarks user upl