Hello, I have the following questions:
1: Is it possible to generate grayscale preview (thumbs) from colour photos?
2: How can I make custom crop of photos?

greyscale is not implemented, but seems pretty easy to do: http://php.about.com/od/gdlibrary/ss/grayscale_gd.htm (check out i.php)

To get custom crops use: getSizeCustomImage(size, width, height, cropwidth, cropheight, cropx, cropy)