Image Uploader: Validate and process images uploaded using forms

This class can be used to upload images uploaded using Web forms.

It takes an uploaded image and check whether the MIME type is of GIF, JPEG or PNG formats, if the file size does not exceed a given limit, or the image width and height is not smaller than a given size.

The class can also create thumbnails and assure that width and height of neither the thumbnails nor the original image exceed given limits.

The original uploaded image and thumbnails are stored in a given directory.